They are not all the same, there are 2 different kinds. You have extenders for non brake solid front forks, and you have extenders for the brake equipped solid front forks. The ones for the brake equipped solid front forks are much harder to find.
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