Ebay often has reproduction holsters.
Here is a black one being auctioned right now that looks pretty good. (I know you said you wanted brown this is just an example)
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1172508345
Just set up a favorite search for "Luger holster" and have them email you whenever one is put up for auction
OR
CMR (listed in the links and resources page of this site) has excellent reproduction holsters in several pleasing colors.
I have examined one of these personally and found the quality excellent.
http://members.aol.com/vf31rhill/90405.jpg