I have had a good experience buying second hand online from https://www.betterworldbooks.com/ and https://www.thriftbooks.com/, they're both good when it comes to looking for used leftist theory books. Other than that I typically just check out my local bookstores or libraries to see if they have any used copies of something that I'm looking for, it can be really hit or miss though.
@morninghymn
@hexbear.net