Gas Cap Gasket

I got my VX smogged, and they told me I need to replace the gas cap as the gasket is leaking. Well, I got a salvaged gas cap and I suspect the gasket for that is starting to go as well.

Anyone know where I can get a new gasket? It's a round O-ring gasket, 2" od, 1 3/4" id, with an indent running along the outer edge.

Id prefer to just replace the gasket, as I cant find any new gas caps that have the tether.

Thanks

How do they know its the gas cap leaking? Is the CEL on? If it is, and the code is for an EVAP leak, then that is the first thing they will recommend, but it needs to be properly diagnosed by a shop. There is a lot of hoses and sensors that can go bad and cause the same code as what they are guessing may be the gas cap. Very rarely have I seen that the gas cap is actually the problem.