Jay 2 the Rescue will have all the right answers.
I used to work in Bethesda, but that was years ago. There was a thrift shop that I used to walk to in the downtown district, but I don't remember the name of the shop, or the street. Check the directory is my best recommendation. The thrifts that used to be in Bethesda were usually very nice because Bethesda is a very affluent area, so they always got top notch donations, and the prices used to be very reasonable. This was, of course before Ebay and the social climate change (where thrifting is now chic). The prices are probably not as cheap as I remember anymore. I used to see nice antiques in the Bethesda shops all the time. Good luck thrifting, and be sure to share your thrifting experiences here. If it turns out well for you I may just take a trip up to Bethesda myself.
-Jay