Arrggh .. this sucks

Offcourse i thought i could trust my friends word when i bought my car two years ago.. rust free unrepaired body... And yes i payed the price of it too
Now the right rear fender from the door jamb to the rear has been replaced -wrong off course - by welding panels offset each other and not seal it anyway to prevent rust. There is rust allready between the panels..
I have to replaced it all. So the question is , where to get "best quality" rear panel ?