New subscriber here. Glad I found you guys.
I don't know how much you guys use Backpage or Craigslist in the UK. If you have a Casual Encounters section on Craigslist, you might simply post an ad. If you post the type of girl you're looking for and ask for pictures (and figure out if they are real or not), you might find a "civilian" who has always wanted to try some bi action herself.
Good luck!