I know some tanning salons have UVB beds. I have no idea if there are studies done for their effectiveness for vitamin D. Tanning beds usually work faster than the sun to tan, so I would wonder if the D production happens more slowly?? Then, you might get tan or burnt before you get enough to make sufficient D. Plus, tanning your skin will age your skin, so even if it works, you have to strike a balance, I know you know that.
Supposedly, UVA and UVC are the most carcinogenic from what I’ve read.
Obviously, I would say read up on it. If you decide to try UVB tanning beds or lamps for D, which I’m not pushing in an shape or form, I would do a very specific experiment so you know. Get a blood test, know your level, do the lamp for whatever time recommended per day per week, and check your level a month later.
Have you increased your supplement intake? I don’t remember what amount you were taking, but I remember encouraging you to take a higher dose and test to see if it helped. Plus, at high doses it’s important to have your calcium checked. I assume if I encouraged you to take more you were taking less than 8,000 IU daily (less than 56,000 weekly).