The thing is, it wouldn't be all equal to begin with, perhaps not ever if you remain married as there are legal privileges you have with a married spouse. You might want to check you're in a State where you aren't likely to be prosecuted for polygamy.
But back to the beginning. It takes time to get to know someone as well as you know each other. And it's unrealistic to expect that affection will grow in the same way in each part of the relationship. Unicorns aren't always just "playthings" - the term can be used to describe the newest person in a triad when the other two have an existing relationship. It's a big shift from one relationship to the 4 relationships going on in a triad:
AB
AC
BC
ABC
You are currently AB. You're looking for someone, C, who can manage to develop both individual relationships with each of you as well as the whole dynamic. That's a big ask from a person. Especially as you're going to still have your core of AB during that. C especially needs skills in being assertive about what they want out of the relationship. Equality is a nice word, but what does that look like in practice? If you intend to cohabit one day would you each have your own room? What about long before that and if you insist on barrier sex with C, or would you all just go get a health check and make decisions around birth control as a triad? Are you already parents? How does this impact C?
But that's a ways off already. Right now you need skills in dating in the real world because as you have experienced, apps aren't great. You literally can walk up to someone and say, "hey, my husband and I practice ethical non-monogamy and we'd like to get to know you better and see if we find a mutual attraction." Thing is, to do this you would have already agreed between you (AB) that this is the person you want to both approach. Already a power imbalance. Already inequality before you've even tabled the suggestion. Hopefully the person would know to ask if you are secure enough to develop the AC and BC relationships separately, and not just expect ABC all the time.
Where do you find this person? Well, places that you find any alternative sub culture. Ren faires and other reenactors, D&D groups (and Runequest), and kink communities are all good places to start IF you have a personal interest in these things. And do a Google search for poly meet ups in your area. But honestly, you're unlikely to find single women as often as you'll find partnered women who are open to having more partners.
On that note, what role models do you have for this being a successful triad? You could meet some successful triads in person and ask them about how they are successful. Gain as much knowledge as possible from those who have done it before. They know it's an exceptionally hard model to develop.
There really is no perfect dating website for this, because
I would not say we are unicorn hunting at all… we want all equal not just a play thing
I understand what you're asking Amanda. I've met a few ladies that are single looking for a couple on BiCupid app. I'm friends with one on Facebook and seeing where it goes now. You read the profiles and weed out the ones that you're not interested in. I'm also talking to a lady from a Facebook page called FFM only single ladies and couples. It has over 12K members. I've tried other apps and sites even sisterwives.com Sisterwives doesn't have many members on it, so I didn't have much luck.