| look in some local junkyards and see what's available. |
You'll be really lucky to find decent door panels at a junkard. On these cars, the interiors (If they are in decent shape) are the first things to be stripped out.
I've been to many junkyards looking for parts. Its common to see 3 or 4 BMWs at one yard with nothing but the interior taken out. And the ones with the door panels still in them are seperated, either from being outside or they came that way.
This is one of those things where you probably can't avoid going to the Dealer. (i.e. that is if you want pristine door panels). Unless you know someone at a yard that can keep an eye out for you.. It sucks but thats the way it is with e36 Door panels..