Hoo boy. Without even opening your profile, I would send a polite thanks but no thanks while thinking "oh hell no." You are looking for a woman no older than a year younger than the younger of the two of you. So, not only are you looking for single women, who are in very short supply relative to demand, you also want to trade up.
I met a couple recently who are fine with her playing while he sits out, but like pretty much every other couple I've known who are okay with this, they're older, have been married for decades, and have been swinging for a long time. In the age group you're looking for, there are very few couples who fit within those parameters. Are the two of you okay with the male half sitting out while the female half plays with a couple? If not, then you understand the problem. If you are okay with that, then I'd suggest looking for other couples on line who are looking for that same starter FMF fantasy. The other possibility is that some clubs have beginner nights. They offer Swinger 101 classes and ask some of their long time member couples to act as mentors. I imagine you might find some possibilities there if that's available in your area.
There are single women who are okay with being a couple's first, but that's a pretty small group for a host of reasons.