where to get second hand parts....

[DEC14N]

Ok just got a 1997 A4 avant 2.8 quattro estate. Needs a few bits doing, rocker cover gaskets, cam belt change, and the alternator needs replacing as im told the bearings are worn out. Been chasing my **** for two days trying to find a second hand one, seems there are a few variations so want to double check im on the right path and also get some ideas of where to continue my hunt for one. Its a bosch 120amp part number 078903015f (i think thats right, 2 different numbers on the label, other is 0123510061).
Any help gratefully recieved!