Just google auto upholstery springs. You'll find zillions of sellers of old fashioned style seat springs - both coil and zig-zag - at very cheap prices.

Figure out how many and what size new ones you need and order them yourself. You can then decide whether to do the seats on your own with a ready-made cover, or find a shop to do it for you.

Here's an example. 10 coil springs for $20 on Amazon. I don't know if these are the right size or not but you get the idea.

https://www.amazon.com/yaaqoo-Upholstery-Pack-10pcs-Furniture-Replacement/dp/B0CFL8ZC7H/ref=sr_1_18


1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)