Need gas cap gasket

[wyopsycho]

Any ideas where to source this? All the gas caps for sale have pictures and no rubber gasket on any of them. I’ll buy a new cap to get the gasket or a paint saver and cap.
Should I just cut one out of an inner tube?

 

[HMAN]

Milwaukee Twins Replacement Gas Cap Gasket For Harley 1936-1982 | JPCycles.com

The Milwaukee Twins Replacement Gas Cap Gasket offers a straightforward solution for securing a tight, leak-free seal on Harley gas caps. This OEM rep…

www.jpcycles.com

Scroll down to "You may also like". Few to choose from depending on your current cap

 

[wyopsycho]

06 mastiff with paint saver.
And thank you