Besides dealers, local gun shops, and members, there is another popular source -- auction houses.
RIAC Regional is coming, take a look (avoid those PRF marked gun, those are totally redone. NPRF marked gun is case by case), search the word "Luger", you will see about 80 of them.
http://www.rockislandauction.com/search/aid/1026
The negative part is the 15% buyer premium, but that's controllable. e.g. your budget is $1800, remove $50 shipping cost, $1750 left, divided that number by 1.15, you have $1521. If found something interesting, max bid is $1500 and control your bid within that, then your max total cost will be $1500 x 1.15 + $50 = $1775.