Call your area beer distributor. Sometimes they retire kegs that have too many dents, etc. Don't do the thing where you buy a keg of beer, drink it and keep the keg. That keg cost the brewery much more than the deposit you paid. Do the right thing and stay legit. We homebrewers don't need any more image problems.
You could also try calling some area microbreweries and see if they have any kegs they want to retire. Scrap yards may occasionally get some kegs, too.