Not that hard to make if you can cut straight and weld (good). Tig welder and the ability to purge is the best way to weld them but other methods will do. I weld sanitary stainless pipe at work often. It isn't all that hard but does take some time to setup everything.
Just cut the stock spring seats in the middle between top and bottom seats and weld in new pipe to make them longer.
The amount of pipe added is about the same amount of lowering you will see in the sled.
That's what was done to the tubes in the above pics. If ya have to pay someone to do it $60 is a good price.
opsled