If you are looking at American aircraft only, try Joe Baugher's site. He has an awesome list of serial numbers by fiscal year and a comprehensive writeup about the designations, etc. For fiscal serials on USAF/USAAF/USAAC:
http://home.att.net/~jbaugher/usafserials.html
He also has a search engine for the serial number so you can look for a particular aircraft type or an individual airplane (Handy with photo identification and research). He also has a site for US Navy and USMC serials.
As an aside, if you are looking to find, recover and restore one yourself, you better have more money than most of us can imagine, must less possess. Restoring one of these old planes is expensive and extremely time consuming. The museum that I belong to has been restoring a B-25 Mitchell for 8 years, and they still have at least 2 more years to go!
If you are interested in being involved in restorations and seeing airplanes fly, try an aviation museum or organization. I belong to the CAF personally, so I am partial to them. Their main page is at :
http://www.commemorativeairforce.org/
They have chapters all over the US and a few overseas as well.
I don't want to burst your bubble on recovery and restoration because there are still aircraft around to be recovered, believe it or not. Getting alot of them out of the countries they sit in depends on local laws and officials. Many pacific island nations will not release any airplanes on their soil regardless of their condition or how much money you have. Some will. The Zero that is at our museum was recovered from Babo airfield in 1991. There are all kinds of little dots all over the pacific and some hold some gems, but the cost of recovery alone is prohibitive. But some have yet to be discovered. Our Zero wasn't actually discovered until 1973.
More info on wrecks and recoveries in the Pacific is at :
http://www.pacificwrecks.com/
They are a non-profit group who could probably be more helpful than NARA. I once dreamed of recovery and restoration of an old bird. I had some searches ready and once I started to look at all the costs, well, that led me to join the CAF. Plus, I get to be around people that share the interest.
Best of luck either way. Keep 'em flying is our motto in the CAF. If you have the financial resources to do it, send me a PM and I can get you in contact with some folks that may be able to help.