I have picked up jars of miscellany from antique/consignment shops many times, mostly because I like not knowing exactly what's hiding in there, and I also get a mason jar along with it. Recently found a squatty glass jar full of bright plastic animals and mermaids for $1.50. I bought an antique can of buttons and got some kid's tooth in the deal. That wasn't fun.
If you search "junk drawer lot" on ebay you can get all sorts of things, but it can get expensive. Also, Alpha Stamps is a good place for assemblage pieces because you'll probably find everything in one place. And don't forget to scour grandparents' houses (or the like) for things they no longer use; a real treasure trove in places like that! Good luck!