It would seem no one has seen Red Dawn, either the old one or the new one.
In the old version, the first thing the occupying force does is go to all the sporting goods stores and find out (through a government mandated form) who owns guns.
Then those people (and hopefully the weapons) are rounded up.
THAT is the problem. The government wants to know who owns what so they can come for the guns when THEY determine it is no longer "safe" (for government) to have weapons,