Y'all know what you want and that is not a bad thing. And you've been out and about and so know that what you want is difficult to find and hard to sustain.
So my suggestion is to stop looking. Not give up but stop looking actively. Instead live your life, meet people, make friends, be social and engaged - in your local poly community and without.
The triads and quads I know that have lasted did so be in part because they often grew organically. Friends fell in love. So many people start their relationship story by 'I stopped looking' and then met so and so.
Live your life, meet people, don't become an isolated couple, explore your interests. You may meet someone(s) who clicks with both of you.
Or you may not. No one is guaranteed anything. It's ok to be frustrated. But avoid entitlement. I am not saying you were being entitled - just that some couples seem to expect 'their' third or other couple to appear shortly after they decide to try poly. This is really unattractive, and also a sign to me if unexamined couple's privilege. It's ok to want everyone to interact all together all the time. And as you know your pool is limited. Some won't do poly. Some won't date couples. Some prefer not to date both people in a couple (like me - way too complicated!). And expecting everyone to be into everyone else all at the same time adds a later of expectations which adds difficulty.
So let go of looking and see what happens in your lives. You may be surprised.