Here are two dealers that have pretty sound reputations with collectors and many advanced collectors I know buy time and time again from both outfits :
There are other outfits out there...some bigger (and some even selling refinished stuff as "mint" and "original")...but I think a beginner cannot go wrong with the two listed above...
You also want to only deal with a dealer that has a 3-day, no questions asked, return policy in writing before you send money.
Tell them you want an original finished piece with collector potential in your price range and area of luger interest.
Simpsons LTD has many WWII luger offerings in their "Mauser" luger section...
Your best bet would be to buy from a fellow collector that you know and can trust, as dealers seem to add their 10-20% mark-ups on price.
If you are a NAPCA member, there is a nice gun show/convention happening in August in Chattanooga, TN...
Email me and I can give you the show details if you are not a member (a member can sponsor your attendance). Always lots of honest lugers that trade hands during this NAPCA event without typical price gouging you see at most gun shows and without the dealer price mark-ups.