I've been to a few amazing gangbang parties in London like https://thephoenixclub.london/, https://londonsexparties.co.uk/, http://www.londonadultpartyclub.com.  They're a ton of fun.

Be nice for group of provider to start one up.    Sure would fill up fast

I've done several but it's SO much work. Now, if there were a group of gents who were already vetted somehow... I'd probably do one twice a month!