Where can I find a punching bag?

I want access to a punching bag but I don't want to get an expensive gym membership and I can't install one in my apartment. I already belong to a gym that I love and don't want to have two gym memberships. I'm also open to taking kickboxing classes somewhere - I used to kickbox a lot and really miss it, but ideally I'd love to be able to just drop in and punch something whenever I'm feeling angry. Where should I look?