wtb: small wooden boxes for tintypes

I have started doing tintype photos at civil war reenactments. My customers often ask about a display case. The only ones I know of are either ridiculously expensive or lacking in quality. I'm trying to make my own, but I sure would prefer just to buy them either pre-made or buy unfinished wooden boxes, paint them black, provide a gold mat and VOILA!
Trouble is, I can't find a good source. I need something that will accommodate 3-inch by 4-inch plates.
Suggestions?