A number of P38s were brought home by Canadian veterans following the Second World War so they're actually pretty accessible to collectors today. If I were you I'd just watch the EE closely as there are usually at least a few examples offered for sale each month. If you're really itching to have one, maybe try putting up a WTB ad.
An original will run you anywhere from $600-$1000 depending on the condition/accessories offered with it so I wouldn't waste your time with dealers who will charge you very close to this for refurbished pistols. There are enough original examples around that if you're patient, I'm sure some fellow collectors here on CGN will be able to help you out.
As far as lugers go, yes, the standard P08 falls within the 12.6 prohib category but you can find ones that have been re-barreled which fit into the restricted category OR if you really want to break the bank, you could go after a WWI Artillery Luger which is restricted from the get go.
- Chris