Cometic makes some really high quality gaskets BUT nobody that I know of makes a case gasket for the 500 or the 250's.

Contact cometic and see what it'd take to have them make AFM (aluminum Foam material) for the center cases.
http://www.cometic.com/custom-gaskets.aspx

This might be a good alternative for people with case problems that would want to weld them back up but are unable to re-surface the centers as nobody currently makes a case gasket for these bikes.

P.S. their AFM gasket thicknesses compresses to much less than their specified specs.