Does anybody know of a reputable dermatologist?

You're joking right?
The word reputable, qualified, trained, professional has no place in the medical profession in China.

There's a dermatology hospital on Renmin Xilu 人民西路 west of Xiao Ximen 小西门 near the old campus of Kunming Medical College 昆明医学院 on the same side of the street.

Their diagnosis and treatment were satisfactory in my case, but they tacked on plenty of unnecessary extras to pad the bill.