Second, the key word is "contract." Just being a member of the military does not give one the ability to buy whatever you want when off-duty. Try that with rocket launcher! The law only exempts purchases made when an official contract has been made between the US government and the knife manufacture/seller.
You can carry any weapon you want if you have a Concealed Weapon Permit
Not always true, and it depends on the state. Most states only apply these permits to handguns, and do not call their permits "Concealed Weapon Permits" as "weapon" is too vague and they are invariably issued for purposes of carrying a handgun. Most call the permit a "Concealed Handgun Permit," "Concealed Pistol License" or variations on those. And those that do call it a "Weapon Permit" do not necessarily allow other weapons besides a handgun in the law itself, so be wary. Why would a permit legally allow you to carry a gun and not something far less deadly? Who said laws make sense!