I don't have any suggestions for specific people a such - all I would suggest is share your gf with anyone that both you and her are comfortable with. So either someone you already know and that you think might be down for it, and that it won't distort the friendship too much or at all. Or somebody new, that either you, your lady or both of you have chatted to first for a time. Long enough to suss if said potential fuckbuddy is cool or not. I.e. clean, considerate and good crack ; D
That's what I'd propose, going off my own experience.