Yes, restaurants and bakery's, as well as grocery stores (not egg flats, but pulp fruit thingies that are like big egg flats), often have them for free if you ask. Otherwise, eBay and bug/feeder sellers tend to have them.
The cafeteria at work saves them for me and I get a 3 ft tall stack at the end of the week. They are usually very clean but I just chuck the ones that have any broken egg on them. This has been working great for several years and I never have to buy egg flats.