Mk IV Engine gasket source

Does anyone know of a source for the squarish gasket that goes between the engine block and the aluminum oil filter assembly without buying a complete engine gasket set?

I attempted making one by hands but must have done something wrong because I was leaking oil out around the top rear stud on the outside of the aluminum housing.

Thanks in advance - Jim

The gasket just made from oil gasket paper, place it over the alloy housing , lightly tap at the edge of the housing with the ball of a ball peen hammer, which will mark the edge and the ball can be used to mark the edges of the holes, the holes can be punched put with waded punches.
Remember one , or is or two, of the studs go though the oil gallery so there is a lot of pressure behind them,
So it’s not a bad idea to use , or make to use a dome nut there to avoid oil working up the thread. Or 3/8" BSF nylon nut if you can find them.
You need new copper or alloy washers . New are annealed . Old are work hardened.
Spring washers will not be oil tight. You may need to spot face the holes in the housing if a Po has used Spring washers … Also applies to sumps.
Be very care , I know someone who decided to put a bolt in instead of the stud. But too long and it locked the oil pump drive shaft.
Gasket against alloy faces should be thin, thick will distort the alloy face check that you oil filter housing base is flat. Asume absolutely everything is bent ,stuffed , worn or distorted until you prove otherwise.

Thanks again Ed. I believe you identified my problem because there was no copper washer on the bolt.

Also need to say an AMEN to you least sentence about everything being suspect until proven otherwise!