You'll need to get the individual seals and such from the dealer. There is no full rebuild kit that I am aware of. Most dealers see the SC as a non-serviceable item but the individual parts are available. I don't happen to have a parts list myself anymore, but I am sure that someone else will chime in with the information you need.
1. One of the most important aspects of a roots type (or any type of rotors) SC rotors are maintaining close tolerances between the blades themselves and the blades to the casing. Too much or too little will cause adverse performance (either failure of the SC or much less boost...can't compress as much air)
2. The two rotors are balanced very specifically to rotate on center in the housing. When they locked up/failed before, any distortion of the blades would cause their center axis of rotation to change and have an imbalance. If excessive, this could cause bad vibrations and destroy the bearings and SC rather quickly. Even if a small amount of imbalance would much reduce the life of the bearings.
On a side note, I'm guessing your problem originated with your bearings getting fried in part or related to not having SC oil. So, whatever you do make sure you maintain the SC oil to extend the life. I just rebuilt a 94 SC about a month ago or so. You may as well pick up some cleaners and soft wire/nylon brushes and clean up the inside of the SC and throttle body.
Yes! Not to dawg on ya or anything, but it sounds like the only reason this went out like that is lack of proper maintenance? Also, letting the coupler (or bearing) go like that for an extended period of time.
Although,in your defense, most places will tell you not to touch it, especially dealers, but maintenance procedures are as easy as changing the motor oil.