I think it would be fun to play with a married couple. They would have knowledge about each other's preferences. I'd like them to show me each other's favorite things. "Look how my wife squirms when I do this." That sort of thing.
There are a lot of couples looking for a female to join in.
I sometimes hang around on a swingers site (it can be fun to chat there) and a lot of the people there are couples looking for a single female to join them. I guess it's a lot easier for couples that are so inclined to find a man who wants to have sex, or alternatively they know that asking for men to join them results in getting far too many unsuitable responces, so you see a lot less genuine ads looking for men in a similar way.
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Anteater, or thanks to CG "Monsieur Manger de Tante"