Where did you read that GM "authorized" Autoform Corp of Elkhart IN to do a convertible conversion? According to page 89 of Camaro the Third Generation, by Michael Lamm they began converting F-body coupes into convertibles in 1983 or 1984. If yours is a 1982, likely the owner contracted with them to do the conversion. FYI, Autoform was just one of at least a half-dozen aftermarket companies that did a convertible conversion on these starting in 1982. Others include Autodyne Corp., Lincoln Park MI, Coach Builders Ltd in High Springs FL, American Custom Coachworks of Beverly Hills CA, John Greenwood of Longwood FL, Hi-Line kustoms Inc of Valley City ND, Duquet-Sawdy Inc of Warren MI, Richard Straman of Costa Mesa CA. ASC designed their version in 1986 and convinced Chevrolet to offer it as an option starting in 1987.
As for any parts to restore your convertible, you'll have to search ebay and hope that someone is parting out a wrecked Auto Form convertible. Otherwise you're out of luck. This is why I always recommend buying the BEST (as in most complete) example you can find. Because the "convertible only" parts just aren't available.
Autoform convertible info
Lon