When we had seals go bad we demoted the cans to warehouse storage of stuff that didn't need to be waterproof. You know, like valves and D Rings and Silverware and stuff.
I wouldn't spend much time looking for a gasket; not sure they can be replaced with original gasket anyway. Might try closed cell weather stripping of the right dimensions, or O Ring stuff, or maybe some of that gasket inna tube stuff.
Or, you can switch lids around if you got a bad can with a good lid or sumpin.
Or, for $20 you can just buy another one. I mean, how much time you gonna spend looking before it costs more to just replace?