For Department 56 (and other similar articles) you may want to check out flea markets, antique malls, thrift stores and second-hand shops.
I get the impression the market's dropped for D56. Where a few years back they were going for exhorbitant prices (collector frenzy, you know) the prices are a lot more reasonable now.
I picked up a number of D56 "Dickens Village" buildings for under $35 each a few years back, just for under the Christmas tree.