Only the 87 trx 70s had the foot brake and they are super impossible to find. There were aftermarket rear brake pedals, but I knew of only one person that had them. You are basically going to have to fab something up that will work for your application.
Nicholson 500x (Project)
Nicholson 185s
Nicholson 110 (That takes an atc70 tank)
Ascott 500 head/350x (Project)
Homebuilt Racer Chromoly Suspension 110 (Ragin Runt)
PK Racing Suspension 70
A+ Inc Suspension 70
AWS Aluminum 90 frame
Hi Performance ATC Suspension frame rd350
Hi Performance ATC Suspension frame 90