Back into the DT forum again after holiday hiatusGarage sales, Swap meet/flea markets, and thrift shops are my main sources because I can't spend too much. I also do some trading. I got my bowed psaltry from a music store in exchange for cleaning out some cupboards and selling tickets to a concert. I always offer to sell tickets or clean up in order to get in to house concerts.
If I'm looking for something particular: The Recycler, an ad newspaper. They're on the web now too. I also tell everyone I know what I'm looking for and someone comes up with it. "Ask and it shall be given". I even tell people who have no connection to folk music. I've answered you in the "instruments" thread.
Our annual folk festival has a consignment booth for people to sell instruments they don't want.
good luck judy