You can find both here:

www.audi.ddsltd.com

The repair manual is $99.95 on CD-ROM (It's the microfiche version put on CD) and the wiring diagram is $40.

The wiring diagram is however possible to find for free!

Here: http://www.autolib.diakom.ru:8001/CAR/Audi/1990/V8%20Quattro/WIRING%20DIAGRAMS/

You should be able to find the repair manual on ebay cheaper but I have so far only seen the german version.

And then there is of course www.alldatadiy.com where you can subscribe to an almost complete service manual for $25 for a year. Its very good, and has the wiring diagrams but is not quite complete but on the other hand the official repair manual isn't complete either and they each cover several things that the other lacks. I use both of them. My repair manual is on microfiche but they are no longer available.

Regards,
Anders