Looking for pics of pre-1975 Cambodian signs or ads for a diorama but can find only Vietnamese stuff. I've tried Google; maybe I'm not doing my search correctly? Any ideas?

You could try to Google Phnom Penh early 1970's it should pull up some signs and ads before the Khmer Rouge.

Many of the smaller shops lining city streets still have signs similar to 70's style, which can be described as "quaint". Most signs then, had French as a second language; now they contain English.