let me understand, your bisexual and looking for a relationship with another female that will not be sexually available to your man, only you as her primarary and her as the secondary and he is ok with it. On the surface it sounds a little selfish to most people, almost being protective of what you have with your man.
To me I would say you are the dominant factor in knowing what you want, and going for it, and know what you dont want and thats ok.
You may want to try looking outside of polly, there are a lot of submissive bisexual females that are looking for a dominant mistress to cater to sexually,
not that you have to be overbaring or treat her like crap (amazingly many people think all submissives want this) its not true.
most bifemale submissives have a real need to sexually serv a bifemale mistress, to give up her control to only her primerary (you) happy to be the seconary knowing your man is off limits to her, unless she is directed only by you to give herself to him, this might be an interesting synario once you have trust and feel you have full control of her and not feel threatened. I think its worth looking at as an option, I personally think openminded bifemales are the best woman a openminded man can have, however its important that your man understands your bisexual needs, need be met in any way you see fit, after all its a huge part of who you are as a beautiful bisexual woman.