I found postcards of Lijiang and Dali at the post office...but can't seem to find any at the post office or the bookstores in Kunming. Am I looking in the wrong places?

Have you tried the bird market?
Just a thought.

just take photos yourself.

many local prof photographers make post cards but they dont come cheap.check local art studios

What about the travel desks at major hotels?

Postcards, what a pain!!!
Brought back memories of sending some to four different people from Dali which never arrived :(

Mandarin Bookshop (WenLin St area) has the best range of posties locally. Not sure any are specifically of Kunming though.