I collect rulers and measuring tools. I probably have a dozen different kinds of wood and metal flat drawered cabinets. Some of the best I have found were library related -- microfiche, card catalog, filmstrip cabinets. Also warehouse inventory card cabinets are good. Government and school surplus auctions are good places to find items like that. Map cabinets are great, but you need a lot of space and plenty of $ to buy them (usually).
The next time I take pictures (later this week or early next week), I will try to take some pictures of my collection and post them in the picture thread so you can get some ideas on cabinets that are out there.