Valve Cover Gaskets
Not sure how thick you’re looking for but I use these on a set of Moroso aluminum (stamped type, not thick cast) and I have no leaks. Have to be careful with the covers being thin aluminum and how much torque is used to tighten as they will bend more so than factory steel covers. And I have no leaks. Also use them on two other vehicles (318 and 360 stock covers) no leaks.
Mr. Gasket 5876 Mr. Gasket Ultra-Seal Valve Cover Gaskets