dude i got mine from cambridge park auto spares. I got a a fun rebuild kit
he sells the seal seperate aswell coz my mate go one
justin
He is in Canada......So I don't think that he'll be hitting Cambridge Pk any time soon
They are not available from Toyota here anymore they have only the outer with no inner (the one that covers 3 spark plug holes). You may be best trying your local parts shop.
OR
Just go into your local Toyota dealership and ask for the valve cover gasket to suit a 1973 Toyota Celica GT (if you haven't done so already).