I know that the prices of these are getting harder to find. Listerstorm and I were scouring the web yesterday to find the few remaining that you don't have to sell your soul to own. I was also trying to find a few T/A donors for upcoming projects. I started on eBay for fun and the prices are very inflated for most of these cars.
Here's some of each that I found at Powerslotcars.com that are in stock:
Grand Prix
Scalextric Eagle Gurney Weslake 1968 Dan Gurney Our Price: $42.95
Scalextric Lotus Cosworth 49 Jim Clark 1968 Tasman Series Our Price: $43.95
Scalextric Lotus Type 49 Jarama 1968 Jo Siffert #16 - $59.95
Trans-Am
Scalextric 1970 Chevy Camaro #33 Our Price: $39.95
Scalextric Smokey Yunick Ford Mustang Boss 302 USA Only! Our Price: $39.95
Scalextric White 1969 Chevy Camaro Our Price: $34.95
Scalextric White 1970 Chevy Camaro Our Price: $34.95
Scalextric 1969 Chevrolet Camaro MauriceCarter Our Price: $39.95
Scalextric 1969 Chevrolet Camaro Todco Racing #7 Our Price: $40.95
Scalextric Chevy Camaro Z28 1972 #48 Our Price: $41.95
Scalextric 1969 Chevy Camaro Bob Fryer #19 U of Pitt Our Price: $44.95
Scalextric 1969 Ford Mustang Boss 302 TransAm Plain White Our Price: $44.95
Scalextric 1969 Chevrolet Z28 Camaro 1976 Sebring #78 Our Price: $47.95
Scalextric 1969 Ford Mustang Al Costner Our Price: $54.95
Scalextric 1970 Chevrolet Camaro TransAm Jim Hall Vic Elford Our Price: $59.95
Scalextric 1970 Chevy Camaro Warren Agor #13 Our Price: $59.95
Scalextric 1969 Chevy Camaro Sunoco #6 ROGER PENSKE Our Price: $69.95
Scalextric Ford Boss Mustang #15 Parnelli Jones Our Price: $79.95
Anyway, cars are still out there, you just have to search.