Before anyone asks here is the cite:
Federal regulations (see below) restrict the sale of automatic knives to anyone other than United States Military, Federal Law Enforcement, Law Enforcement, Fire, Rescue and EMT personnel with acceptance of the "Auto Knife Opening Acknowledgement Form".
18 USC 1716 (G) (2) (1-4) provides this summary: Switchblade knives can be shipped to civilian and armed forces supply or procurement officers and employees of the Federal government ordering or procuring or purchasing such knives in connection with activities in the Federal government; to supply or procurement officers in the National Guard, the Air National Guard or militia of the state or territory of the District of Columbia ordering, procuring or purchasing such knives in connection with the activities of such organizations; to supply or procurement officers or employees of the municipal government of the District of Columbia or the government of any state or territory of any county, city, or other political subdivision of a state or territory ordering, procuring or purchasing such knives in connection with the activities of such government.
15 USC 1244 provides in summary: Knives can be shipped by common carrier, that sale, transportation or distribution, possession or introduction into interstate commerce of switchblade knives is authorized if it is pursuant to a contract with the armed forces or any member or employee thereof acting in the performance of his or her duty may possess switchblade knives any may have them shipped to him and sold to him or her. The possession and transportation upon his or her person of a switchblade knife or a blade 3 inches or less is authorized to any handicapped individual who has the use of only one arm.