Peter-
I have both silicone and black masks. Both obviously work, but with the silicone I get some peripheral awareness, and I enjoy that more than wearing the black "blinders" from a rubber mask. Given the choice I prefer the silicone. If the best fit was black rubber...I'd still go for the fit.
There will never be a lot of ophthalmologists or opticians working with masks simply because there is not a lot of work to go around, not enough to support a lot of practitioners. But given the costs of shipments in and out of the US, I strongly suspect you can chase down a more local source of expertise.
My first mask was never intended to have lenses installed in it. And being somewhat of a shallow profile, that made things easier because the lenses were closer to my eye, and also harder because a low volume mask has less room to install thick lenses. I would think you want glass lenses installed, for the same reason we have glass masks, to prevent scratching. But glass lenses (at least in the US) are getting harder to find too, they cost more than plastic. So you may find practitioners telling you "white lies" about what they can and cannot offer and do.
But somewhere out there, you should be able to chase down someone you can work with. If you have an eye doctor that you have a working relationship with, tell them what you are looking for. Ask them how this can complicate things, and what kind of questions (distance from mask to eye, distance between eye centers, etc.) a professional should be asking you for. I wouldn't expect critical vision as I would want from glasses, but something "good enough" for an our or two, the way that "reading glasses" from a pharmacy are "good enough" when you just need to read something, possibly for a couple of hours.