Yes.
http://clarkcopperheadgaskets.com/cchg/modules/content/?id=1
http://www.scegaskets.com/
Hussey copper used to have them. I brokered a group purchase a few years ago, but they have shut down.
A google searce will turn up a couple of other companies, but I don't know if they have slant six gaskets.
I have used Hussey and SCE. Never used Clark, but have talked to them since Hussey shut down, and would try them, next time.
