Bobtheseat used to sell them, I think. However, no sign of any ebay activity from him recently - I know that he sometimes goes offline to catch up on orders.
A couple of things:-
1) If my eyes don't deceive me, and with my anorak very much on and rivets being assiduously counted
, those might be 1976 clocks (clock face had a greener tinge than later years). I can't be sure of the colour of yours, though.
2) Your existing cover doesn't look too bad (starting to split along the seam?). However, you might open yourself up to a load of pain if you take that existing one off and then find a lot of the seat base edge has been nibbled away by rust.
