To find a gf who is into the idea of sex with 3 relative strangers... find one who has had group sex experience already, and is open minded/kinky in general. There is absolutely no guarantee she will be attracted to everyone in your V, however. All the stars have to be aligned and conditions just right. Group sex where one or more of the participants feels the least bit pressured or coerced is a recipe for disaster down the road.
Steve should plan to date her a good while, just for her and for "love," before expecting anything more in the sex department. Having an ulterior motive is kinda icky, imo. Sometimes metamours don't even meet for months, much less hop in the sack with them!
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
me: Mags, 59, living with:
miss pixi, 37