Unfortunately, kartek doesn't show everything they have in stock on their website, so you'll have to call to order them, just picked up a set from them a few weeks ago.

Replace the bushings and see if that cures your problem...
As for the big nut, there's a guide behind it that keeps the rack main shaft tight, there's not much adjustment there, unlike the older gearboxes, so you shouldn't need to touch it.

The rack can be rebuilt, but in most cases, it'll cost more in parts, than ordering another one. Example the seal kit cost $76.49, guide $76.01, inner tie rod $98.77....etc....