Thrift stores (also fun) were my other searching grounds - this time for silver(ish) photo frames. In a black & white show, it's silver that you need. I'm actually a little worried that some of the silver I found is a little "off," a little too warm and golden in tone; I may have to spray paint them more silver.
Believed public domain photo messed with.
Trying to avoid all color and tinting? To find true black, white, or especially gray? Very difficult. Look at the world around you. That black? Tinted navy blue. That white? The faintest possible pink. That silver? Slightly, slightly brassy.