I bought up a bunch of SBP parts while they were reduced in price for future builds. Sprockets, bracketry, HD freewheel and a bunch of the hd bearings, etc. Some of that stuff you can easily buy yourself like the 5/8" keyed shaft and their bearings though.
That being said, a shift kit really isn't necessary with most builds. Simply pedal, start the motor, and ride. The shift kits add a lot of complexity where it really isn't needed, and the sheer number of gears and their narrow spacing are also a bit useless. You spend a lot of time shifting for minor changes in speed.
The only reason I want to hang on to this stuff is because I still want to do a shift kit build with a 3 speed internally geared hub, but with all of the chain in the system being 415h for proper durability.