Below is the standard and optional parts for the super nitro. The spur gears are getting scarce and pricey. I bought a few of each and paid 5$-18 each.
If you have a 3d printer, I can get a few links. They cost a few bucks, but you can reprint as needed.
I'm gathering part numbers. For the 2...
The part I linked is for a shaft. Ill try to see the parts for the belt and see what can be used on each.
That seller I linked, pm him and tell him you have a belt rs4 and am looking for a 2 speed. Hes one of my plugs so to speak. I think he finds sweet rides and parts them.
Maybe try tgis one?
https://www.ebay.com/itm/125452835440?hash=item1d35925a70:g:RnkAAOSwzqxi7-ht
I just bought titanium rs4 parts from them a week ago.
Nitro rs4 parts are hard to get. Super is more rare. You probably see where this is going. You gave any pics of it? I always wanted a super rs4.