If a heterosexual couple looking for a bisexual woman is looking for a unicorn, would that mean that a couple looking for a bisexual man is looking for a centaur?
I mean...I guess? To my knowledge no one has come up with a word for that yet, so if you're in that situation and want to label it that way, go for it.
I'm not sure we need a parallel fantasy-creature term for it, though - the word "unicorn" is supposed to imply that "a bisexual woman who is attracted to both you and your partner and wants to date you on your specific terms and is willing to engage with all your baggage and perform the emotional labor that comes with you two opening your relationship" is incredibly rare (perhaps even fictional) and requires lots of patience and effort on your part to find. It's a term born out of necessity, not just to be cute.
So I'd want to hear from bisexual men who have been sought (or "hunted") about their needs, and what frustrating patterns or blind spots they've seen in the couples seeking them, and what term they think captures this well.