Hercano Propulsion (spelling wrong) run by Jerry Biro (his wife Linda does the work, uh, make that administrative work!) has all the necessary parts, including gasket sets. His prices are very good, and they are professional. Do a search of this sub-forum and you'll find several posts made by me with some contact information for them. (They are in Ohio.)
Q: how did you end with a blown head gasket? (Curious...) And does your generator have an ASK?
Here you go:
JERRY BIRO
P.O. BOX 206
MARTINSBURG,OH 43037
740-745-1475 fax 740-745-2475