You mean the mechanical speed control or the electronic speed control (that came with the re-released version of the car)?
I'd suggest you just get a cheap new electronic speed control instead of trying to get back the old mechnical one (if this is the one you are looking for).
Of course - the gear ratios of tractor trucks are much higher than pajero. Even if you use mechanical speed control the car will still run much faster. And I don't think it can use higher gear ratio (the smallest pinion gear that can be used is 16T).
Other C-hing may have ideas for you. I am out of ideas. Sorry.