UNFALLWAGEN Suche Deutschland!

https://s2k.de/www.mobile.de
https://s2k.de/www.autoscout24.de

Usual pages for used cars, but sometimes there're also crashed cars.

This might help you (maybe):

http://www.motoso.de/
http://www.kiesow.de/teile_shop_2.php

I´m not absolutely sure, but I think Motoso sells used parts.

Alex