Aside from amateur stuff, it's hard to find porn dedicated to this. There are lots of amateur videos of guys juicing themselves alone (which doesn't do it for me) and some stuff with couples, but the guy is often masturbated to orgasm while his ass is fingered. Hot, but not quite the point of this thread.
However, but I have found 4 scenes where a group of Japanese girls each take turns pegging a guy with a strap-on dildo. And the men each enjoy a genuine hands-free orgasm in each scene! The only downside is that because it's Japanese porn, the pegging is censored. Anyone interested will have to search the 'Net for it, as I cannot provide the links on this forum or in PMs. The addresses will get edited out by Freeones.
OK, there's a chance that those videos are edited, and the guys involved might have got themselves to the point of no return by masturbating and the girls simply finished their man off each time with the assfucking. Either way, what you see in the videos is that the guy getting his prostate tickled to orgasm by the babe pegging him, and that's fucking hot!