I prefer the cork gaskets too but they are getting hard to find. Napa shows these
https://www.napaonline.com/en/p/FPBVS30055C
The last Fel Pro's I bought were listed as cork but when I opened the box, they were rubber.
You may have to hit up the restoration companies like Ausley's, Year one, or even corvette shops to find "correct" original cork gaskets.