Crankcase Drain Plug Gasket

The small crankcase drain plug on my 74' 850 Commando currently has a nylon or plastic washer on it and it is cracked and split. I don't think that this is the correct washer as the Andover Norton parts microfiche calls for part # 062624 and shows it as a copper washer.
Is there a reasonable substitute that can be used or obtained at a hardware store or auto parts supplier?
Or should I try to get the copper one that AN calls for?

Yes. Fiber and aluminum. I like an aluminum washer rather than copper used when against aluminum.

Harbor Freight sells a box of assorted copper crush washers. In a pinch use thread sealant.