Well, most bi poly women don't want to join a couple that only comes as a package deal. While, yes, there are women who enjoy and are turned on by the idea of being involved with a couple, they usually don't want a pre-packaged situation that they're expected to "join." There is no way to guarantee that someone will be attracted to and compatible with two people at the same time, so it's rather unreasonable to expect that. Since it's basically an impossible, futile hope, the woman you're looking for is known in poly circles as a unicorn - because unicorns are mythical and don't actually exist. You might find someone interested in threesomes and recreational sex only, but I am guessing you want a committed triad relationship since you posted here at a poly forum.
If you are open to each of you dating separately, and/or don't have idiotic rules like she can only have sex with both of you at the same time and never one-on-one with either of you individually, OR that she isn't married or "allowed" to also date others besides you two, then you'll have a much better chance of meeting someone. Here are some threads you might find informative and helpful (you can set your preferences in "User CP" to view 100 posts per page, which makes it much easier to read long threads) :
Added to, Joining In
Unicorns & Unicorn Hunters - Merged Threads, General Discussion
What is the appeal of a unicorn?
What's in it for a unicorn?
the unicorn and its hunters
I would also do a Tag Search here for the word "unicorn" and the phrase "unicorn hunters" or "unicorn hunting." Please especially take to heart what has been shared in these threads by the bisexual women who've been targeted by unicorn hunters or who have come out of failed triads. BTW, most triads that start out by people looking for someone to fit into a role of "Third" (rather than developing organically out of meeting someone who clicks with one of you and eventually over time things develop with the other partner on its own without having been expected to go that way), implode disastrously.
Triads are the least stable relationship configuration in polyamory.
Hope this is helpful!