The one that does come to mind which is arguably the best one is the one between Mia Malkova/Danny Mountain and Anikka Albrite/Mick Blue. I'm not sure what it was shot for but it can be found on two Adam and Eve compilations: Swinging Away and Couples with Benefits.
It's much easier to find real life porn couples, dating or married, in a threesome with another guy (or girl).

