I have never met anybody on Zity or any other fetish site. Back in 2006, I befriended a girl who was awaiting a lung transplant. She was thin, with long brown hair, and 5ft6. She modeled on deviantART. She also wore a mask to protect her immune system and lungs.
I confided in her one day that while I would never wish cystic fibrosis or any disease on anybody, it was a turn on for me that she had to wear her mask in public, and often even modeled in it. This mask fetish of mine is lifelong, and does apparently derive from the fact that I have spent so much time in the hospital myself. It's my medfet.
Anyhow, we stayed in contact over the year, and eventually met. She had two masks with her that night. The moment I met her in person, she had on her face a white earloop mask with a white lace pattern, by I Can Breathe. But soon, she switched into a North 5500 half mask cartridge respirator. Big dark greyish/blackish/blue silicone mask covering her mouth and nose. Thick black straps to keep it tightly on her face, and huge, circular filter cartridges sticking out the sides, covered with a white prefilter.
Medfet is kind of obscure, or at least hush-hush, and my particular medfet of girls wearing medically required masks is even more so, even on Zity. So, I don't envision myself ever meeting up with a girl from her. I think in my case, fantasy world is (sadly) better anyway.