Go visit an upholstery supply shop; I'm willing to bet they have a kit to replace the springs, or at least most of the parts. While you're there, get a set of hogring pliers and a box of rings for installng seatcovers. They'll also have raw cotton padding of varying thickness so you can replicate stock lumps if you so choose.
Seatcovers are everywhere (ChevyDuty, LMC, etc.) or you can pick your own fabric and make your own.
