You can find part numbers from your dealer.
I am, probably like you, adding options to my 2002 e46. I have found a lot of bargains on salvage yards (junk yard). I have bought parts from junk yards on the internet, that only I knew where they come from: my friends were sure, I got them from dealer. Just make sure you have them e-mail you picture of the part, they going to send to you before you buy and if possible with OEM part visible.
But be careful...