Three some

So I need opinions, me and my boyfriend have been together for over a year. Recently we've shared ideas about a threesome, I'm bi sexual so I like women and men and we decided we'd would try a three some with a women. The issue is neither of us know how we can go about finding a partner. What do y'all think? How should I go about finding a partner for us? He told me it'll be my choice of who I want I just don't know how to go about finding anyone.