IMHO, nothing good, I´m afraid.
However, here is link to one shop a bit away from the city center, but you can still take the tram.
http://www.kvibergsoverskott.se/
I was there in July and it´s mostly crap nowadays.
If you have access to a car, you may try A.L.E in a very small village called Slutarp, some one and a half our away from gothenburg -
http://www.surplus.se/. No public transportation as far as I know. Even though their stock is smaller every time I get there and the prices are on the rise, they still have some good gear för sale, actually more than their website indicates. Only open at limited hours, however.