I too have had mixed results when trying to get replacement oil-plug
gaskets for my various vehicles. Costs have varied wildly also, with one
or 2 gaskets costing up to a buck or 2 each! Recently, I found that
Winchester Auto on Winchester Blvd, in San Jose, CA, has a box of  110
copper washers (assorted metric sizes) for about $20. Far more than I
need/want, so if anyone wants to split a box of these, let me know.
Cheers, jt (in Campbell)