When did aftermarket racing style bucket seats first appear?
Here are some aftermarket racing style (to differentiate them from custom type bucket seats) found in 1/24 and 1/25 scale kits, and a list of the kit(s) in which they were included (click twice on the image to enlarge):
Revell '56 Chevy
MPC '69 Mustang
Revell Henry J, Willys pickup, Austin
AMT '70s Chevy Camaro kits
AMT Competition T-Body Parts Pack
.
AMT '69 Corvair
AMT '69 Chevelle SS 396
MPC '67 GTO
.
AMT '55 Nomad
MPC Mustang II
AMT Wynn's Jammer
MPC Pro Stock Chevy Vega
MPC 1967 Bonneville - Hardtop and Convertible
.
Revell Parts Pack, '31 Woody/Tudor/Sedan Delivery