If you are using industrial type air compressors, you can expect your compressor supplier to have a full range of spare parts for you, including any gaskets you may need.
This will likely not be the case for the lower cost, DIY type air compressors, that are being sold by the thousands from big and small box stores throughout North America (and the world??). What to do if you need a gasket?
Recognize first of all that a compressor pump head gets very, very hot in operation. Yes, you can burn skin with the heat generated, so any gasket material has to be heat resistant.
They acquired gasketing material. They disassembled the pump and located all the gaskets that were present. They then either removed them to use as a template to make new ones, or used the surface where the original gaskets were installed as a template, if the gasket was beyond removal in one piece. With the old gasket template as a guide, they marked the new gasket material appropriately, and cut the material to suit.
If your air compressor won’t build pressure past a certain point, the most frequent causes seem to be either the intake or high pressure reed / flapper valve is failing, or a gasket is letting go. You may, nor may not, be able to see the failure point if it is the gasket. Yet, once you have the pump apart, you might as well eliminate that as the potential problem, by installing new gaskets.
If you can’t buy them, you can make your own.
I have not dealt with the company myself, but a source that has popped up for gasket material is:
I don’t think you can buy from them, but you can find the material and a source through them, evidently.