There are certain parts of the Eaton SC'* that are not available through any other source but Eaton and Magnusson. The input shaft, output shafts, rotors, and gears are some of those parts. If you can't get a replacement unit to cannibalize from a junkyard, you'll either have to replace your nosedrive, or pray that someone has one on the shelf. Try www.canadiansupercharger.com
to start with. From there, I'd go right to Magnusson, but I wouldn't bet they'd sell you just the shaft.