Yeowy..that a toughie. Since you took your bike to a shop, hopefully they can bang/grind them out. Other than that all I could suggest is hitting: flee markets/want ads/Craig list/Ebay etc etc etc....
Good Luck
Seems like Schwinn started equipping the Deluxe models with S-5/6 wheels and tires starting in 1971. The 1970 and earlier Deluxe Twinns were equipped with S-7 rims and tires, and the standard Twinn models had the S-7's through all years. It would seem to me that the wider rim and tire would be the best choice for all Twinns, and I can't see where going to the slimmer rim and tire on just the Deluxe models would provide any advantage to Schwinn or consumers.