Craigslist/fb marketplace can be a good way to find garage sales so you dont have to negotiate a meet up time / place or anything. Also look for estate / moving sales. Check along local roads for signs on upcoming garage sales.
Thrift stores can be ok but can be expensive or not have great stuff if its in an expensive area. Consider going to smaller shops / delis and looking for if they have a section for local business cards; some places will have a section where people will leave a stack of business cards, so you might be able to find smaller thrift/antique shops that way, or find an ad someone has left for upcoming sales.
Also check: local facebook groups, local library in person / website
Not sure about other online sites or specific items though.












I can’t find it right now but if I could I’d post the one about the ancient greek or roman dude with a interest in ships that would watch them enter and leave port and knew each one by name