They are not common, many girls I have BFE to go white when you ask them either if your wife could come down alone for a massage, or if you could bring wife there for a couples'. They have something about getting up in your family biz and don't want to meet your wife.
BUT. There are two that do this, I took my wife for her birthday earlier this year. Only because it was what we wanted and asked for, it was that my wife got a fourhands with happy ending, while I relaxed on the chair and watched. The girls were puzzled that we did not want a couples' massage to go with it, but they were fine with the action. I don't feel comfortable naming the places, they were rather clear about this.
But look, lots of places in the area do couples' massage and have table for it. For me, the place we went to for this was place that I had lots and lots of YMMV points saved up, and from how many times we chatted about my wife and even they texted mit her sometimes, they knew her well. She had also been there a few times as a customer on her own. So, whatever place you go to a lot, have lots of built up credits there, and know the girl(s) well, it doesn't hurt to ask. Best way is at one of these places, ask first, "my wife always hears about how great you girls are here, she wondered if she could come here and get a massage and same service?" For provider, this is an easy yes or no question, either they jerk ladies off or they don't; I'd find it hard to believe one that you have some relationship with would have a fit over the question alone. I've asked many times to many providers (all with "no" except these two), and all went on with normal operation right after as if nothing happened.
They're put off by female customers often because female customers tip them like how they tip at Hand and Stone, 20 bucks for "outstanding service", more likely ten bucks. As you know from mongering, if you were to set a single Jackson down as you are undressing and the lady came in to start massage and spotted this, you'd be lucky to get a 1 out of 10 massage and the worst jackhammer ever if anything.
Just as likely that the two places we did this at wouldn't even talk to you about it. I just don't think general Chinese AMP ladies do lesbo stuff. One I know explained to me that she had a female customer right before I got there, and the customer acted just like how we would, you know, OTC and even UTC, trying everything to get the girl to give her a HE, but the provider never relented. Will not be an easy nut to crack. Closed mouth don't get fed though.