They do, but are fewer and further between. Research studies have shown that there is a much higher proportion of bi/pan women compared to men in the US. So a triad with two bi women is gonna be much more likely to occur than one with two bi men.

"unicorn hunters" are a well known trope and generally looked on with scorn within ethical non-monogamy / polyamory communities. They're almost always a bad kind of hierarchical, and usually don't see the new third person as an equal, whole, person.

I'm going to guess that bisexual men looking for another man are slightly less likely to be this particular kind of dehumanizing, but I don't have any data to back it up.

The bi guy-straight woman couples I know are largely just “he’s welcome to sleep around with other guys but she doesn’t want to”

The guy just makes a Sniffies profile and hooks up on the side. The one in the photo I mean.

We're too introverted to ask.

Well, hubs and I would love another man to want to come in and just be in charge of both of us, but we're also not looking, so...

God, I should probably post this on my alt but fuck it. Women being bi is more socially acceptable than men, but no way are more women than men actually bisexual. But yes, men willing to threesome are easy to find, straight or bi. Women who want to MFF are less common, therefore they are unicorns. And no I don't understand it because which is sort of threesome more fun for everyone? Obviously it's the two men, one woman sort. So many possibilities!