Some of those cars were provided by the manufactuer, like the "Knight Rider" Trans Am and Jim Rockfords Gold Firebird Esprits and his fathers GMC's, but some of the cars, like the ones on the "Dukes of Hazzard" I dont belive were supplied by that manufactuer, If you really look at the cars on the show, it;s like they raided a used car lot for all the cars, I think that the newest car on the show was Daisys Jeep, which I think was like a 78 or 79.
The Charger was a 1969
Boss Hogg Cadillac was a 1970
The police cars were various vintage 70's Plymouth-Dodge, or "Plodge" Furys and Monacos, except for the 1st season, when they were AMC Ambassadors.
Cooters GMC tow truck was like a 1974-1975
Uncle Jessies F100 was about a 1972 model.
I do think that GM did supply the GMC van and Corvette for the "A-Team"
Ponch did have a Firebird on "CHiPs" but it was like a 1971 or 1972 model and the show came out in the later 70's, so I dont think that it came from Pontiac, but remeber his partner, Baker, had a GMC Sierra 4x4 Sportstide. All the police cars were "Plodges" too.
I think that their big sponsor was Kawasaki, who supplied the bikes.
I dont know how they got the Ferrari for Magnum, but it sure was cool, especially the shot in the credits at the begining, where he takes of with the Ferrari on wet grass and fish-tails the car on to the road.
Trivia question? What did everyone else on Magnum drive? i.e all the other characters...\
Bonus: What was on the Ferraris liscence plate? (easy)