hub shell replacement (DT Swiss)?
 

So I 've got a pair of hubs that came on my '02 Supercal. OEM DT Onyx(?) 24 hole front, 28 hole rear.
I can't find rims for them stout enough to build up for XC ridiing on my 29er. The Bonty Race Lites that came with are out of production. Rather than selling them as 'Cross hubs, it's been suggested that I try to swap the shells for 32 hole models.

What's involved in this? Are replacement shells even available? Is it a cost effective maneuver? Can I do it with proper tools, or is it a back-to-the factory type of affair?