The ReStores around me seem to sell whatever they can get their hands on. Last time I went, I got an ElectroPak 35w HPS wallpack of 1980s vintage. Every time I've gone, they seem to have something interesting, and they don't have a problem with selling fluorescent or HID lamps/fixtures. However, they don't have particularly high prices, and the items are usually on sale.
The two Goodwills near my house don't seem to care about mercury content in the products they sell. Both of them use traditional means to light the stores - MH in the parking lot, F32T8 or PL fluorescent indoors. Only one LED in sight - a small strip lighting a convenience cabinet. You can usually tell which thrift stores care about mercury content by the lighting they use - if it's converted to LED, it's unlikely you will find anything. This does not always hold true, as the Value Village down the way doesn't seem to care either, and it's converted fully to LED (except in the parking lot, where it's MH.)
I've found that thrift stores that are run by churches tend to have very good prices. There's a place called PACS Thrift in East Portland that sells things at bargain-basement prices. They usually have some very interesting things in regards to lighting. It was there that I found a 275W SBMV reflector lamp. Now THAT was quite a find!