Search upholstery seat springs, Couch springs, coils springs, zig zag springs, etc.

You will find every size and shape coil spring and zig zag seat spring you can imagine.

I've seen packs of 10 or 20 for Like $30 or $50 . They'e on Amazon, ebay, etc.

Pull out some of yours and measure them. I think they're about 7" tall.

Here's a search result: https://www.google.com/search?client=firefox-b-1-e&q=upholstery+coil+springs

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)