I don't see any reason why the local Audi dealer can't find a part number. Try another dealer, or check a VW dealer for a 6 speed 4Motion application, '98 to about '03. Same for an Audi application; '97-'04 Quattro 6 speed. I believe all 01E's use the same slave; it's the plastic one with that funny quick disconnect fitting. The problem with it that I'm aware of is that unless you spend $100+ on an Audi/VW hose assembly, there's no standard quick disconnect that will work to adapt to it (anyone?).
I'm using Audi P/N 4A0721261, which is not an 01E part (I need to verify that part number just to be sure). It has an aluminum body with the same anchor position as an 01E and the same fitting size as the 016 slave cylinder. It fits the 01E. I belive its' application is an Audi 80/90. It does have a very slightly smaller diameter piston that the 01E slave. I chose it because it will be easier to adapt the hydraulic line (also lends itself to modification, if necessay).
Andys