Halting Gun Sales to Government

"And while the biggest arms dealer in the world is your boss - the president of the United States, who ships more merchandise in a day than I do in a year - sometimes it's embarrasing to have his fingerprints on the guns. Sometimes he needs a freelancer like me to supply forces he can't be seen supplying."
--Yuri Orlov (Lord of War)

In the wake of various government efforts to increase gun control, various arms makers are curbing sales to various government agencies.

If enough gun and ammo producers ceased selling weaponry to the federal government, is there any doubt that the government would commence gun and ammo production (or expropriate productive assets from private hands)?

Without guns, government has no authority.