One of the best resources is the internet, of course.
However, I've had most of my luck with materials by buying magazines - there's a surprising number about various aspects of home renovation, and of course, there are lots of ads.
FYI, I'm looking at Chelsea Decorative Metal tin ceiling patterns. I found them, Snelling Thermo-Vac, and aa-Abingdon (I don't know if I have that name quite right) from magazine ads.
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