1. There are currently 140,000 registered firearms sellers in the United States (source: Arming America, Origins of a National Gun Culture)
The statistic information above should be explained further. According ATF publication "Firearms Commerce in the United States: Annual Statistical Update 2014", there were a total of 139,244 Federal Firearms Licensees (FFLs) in fiscal year 2013. This number has been steadily climbing since 1996. However, the number of licensees peaked in 1992 with 284,117.
Furthermore, the term "seller" is not accurate. The number cited includes licensees who are not considered "sellers" of firearms; collectors of firearms and manufacturers of ammunition. The state with the largest number of FFLs is Texas, with about 10,500 FFLs as of fiscal year 2013.