The Lloyd Sealy Library at the John Jay College of Criminal Justice collects materials on guns. Also, DBI Books (Northbrook, Illinois) puts out a line of materials about guns (e.g., Gun Digest Book of Free Arms Assembly Disassembly).
Federal gun laws are administered by the Bureau of Alcohol, Tobacco and Firearms (ATF). You can find Federal gun laws, regulations, proposed regulations, statistics and the lists of recognized collectible guns, known as "Curios or Relics," on the ATF Web site.
The ATF's FFL eZ Check database lets gun sellers verify that a gun buyer's Federal Firearms License is valid.
The Legal Community Against Violence posts a summary of State and Local Gun Laws, with citations.
Stolen Guns: Generally gun buyers have to call the police if they want to know if the serial number of a gun has been reported as stolen.