I'm a straight CIS man, not yet old.
FYI, it's "cis" - not CIS. I'm cis, too.
"not yet old" probably means something different to each person that says or reads it. I hope you won't give up when you decide you are old.
I've always wanted polyamory, but even before my circumstances got bad, finding just one woman was so infrequent for me that more than one wasn't realistic.
You don't have to find more that one woman to be poly. You can be poly and not dating, poly and dating, poly and committed to one or many, and any combination of these (and probably other things). Are you saying you have always specifically wanted to have long-term relationships going with multiple partners/lovers/women?
What is it you want from polyamory, or from relationships in general? Are you looking for someone to live with (a "nesting partner"), with the option to have multiple loving relationships?
And (I live in a poly mecca) the poly personal ads often say no poly first timers.
If you live in a poly mecca, you can probably meet poly folks lots of places besides the personals ...
Read up on why people are wary of starting relationships with poly newbies. Address those potential pitfalls with yourself now, and wow your new poly contacts with the homework you've done.
But now, bottom line, being someone's poly secondary relationship has become the best (and perhaps still more than) I can hope for.
The circumstances that make this true are unfortunately insoluble.
I think you have convinced yourself of some absolutes that may
feel accurate, but cannot logically be so. You can certainly hope for and pursue relationships that can develop into what you're looking for. But you might have to think outside the box you've drawn.
There are plenty of poly people who don't do primary/secondary. Does your preferred polystyle involve "being someone's primary"? Since you seem (above) to say you've wanted to have multiple concurrent relationships, have you imagined being primary to more than one person, or having a primary and a secondary relationship?
One thing many experienced polyamorous people will tell you is that prescribing the only type of poly relationship you really want, then trying to fit people into those roles (or considering all other configurations inferior), is the harder way to go. Letting relationships be what they are, and accepting (or rejecting) the shape they naturally (or at least comfortably) take might be a more realistic approach.
Regardless of what kinds of relationships you see as ideal, or an end goal, every relationship starts with meeting someone, getting to know them, and finding out if you both want to explore the same possibilities.
I acquired a daunting array of serious medical issues and disabilities which severely limit me physically (though not sexually), finanacially, and timewise.
My extremely limited time has put off the few dating prospects I've found...
My circumstances have also isolated me socially.
So, you seek people who can work within your severe physical limitations, your scarce time availability, and your financial constraints. These are huge challenges.
Finding people is about networking - getting "out there" and being social, while doing what you like. Even if this has to be partly or mostly virtual for you, there are plenty of ways to find people who like the same things you do, or like to spend time the way you do. Once you meet people, chemistry and compatibility filter some of them closer, and as you get to know them relationship potential becomes apparent. (also see below, regarding the friend zone)
(of course I dialed down my 'standards' of who I was looking for).
This confuses me. Why would you actively seek people who aren't what you want in a partner? If you think they could still be long-term potential without meeting your initial criteria, then are your initial criteria reasonable?
I'm curious about what these standards might be. If the difference is complementarity (I can't do some things which one person will have to be able to do for us to meet up), I get that. But you used the word "standards," like you have in mind specific minimum levels of desirable qualities. If you projected these standards onto others, would you meet their standards? Are you able to be the person you want to date? If not, what could you do to be that person more, or to give potential partners the chance to prove compatibility regardless of your elements of ideal configuration?
While I wish I could be more than secondary, it sounds a lot better than being 'friend zoned' (which I've experienced more than my share of), or the 'neither' that I have now.
"More than secondary" and "friend zoned" sort of imply that there is a place you should be in someone's life, when they don't also want to offer you that role. Secondary partners and friends don't have to be seen as "less than".
I get that you want(?) to be someone's primary partner. You want that person to be poly (or to accept that you are and plan to be). The only way to find out if you have long-term potential *as a dyad* is to connect and see what you both want to do. This will not always be shacking up forever in primary poly bliss. If you are willing to ever be a secondary (for instance, even after you find a primary partner), then accept the potential for being a secondary with each person you meet. Maybe you find your lifelong secondary partner soulmate before your primary. Is that so bad? Maybe you have some shorter term relationships that aren't any of them long-haul runners. What is lost? You're not old yet!
If you truly don't have time for friends who know they don't want a more intimate relationship with you, I guess you'll have to decide how much you want to invest in getting to know people before you will somehow test their potential. Be honest with yourself and them about what you're looking for, and move on without blame when your goals diverge. The "Friend zone" isn't purgatory that someone else is putting you in. It's in your head, from your expectations. If someone says there is potential, and you don't see the potential developing, it's on you to clarify and cut loose, if that's your game. To be clear, I don't think this is the best way to find love and support in this world, but if it's your way, own it and respect your own boundaries.
I imagine that my motivation might be greeted with disdain, as I have only finally decided to look to polyamory as a 'last resort'. But I truly have always felt it in my heart.
Is your immediate motivation at all important if you're finally being authentic to who you are? Do you see polyamory as "less than" monogamy, as you seem to see "secondary" and "friend" as lower value relationships than "primary"? If you're not embracing polyamory enthusiastically, you probably want to unpack that (or risk being the nightmare poly newbie the personal ads hint at).
Read "More than Two." Explore Relationship Anarchy. Decide if you really feel polyamory in your heart.
Good luck. I think you have some more talking with yourself (or maybe a counselor?) to do, to figure out what you want, and how to approach others with more curiosity and less specific expectations -- a formula that can allow both them and you more agency.