I know people with hundreds of thousands of rounds of reloading supplies, some with as much ammo.. They're not unique.

We've been making "modern" repeating firearms and ammunition for over 100 years - it's foolish to think that with modern precision technology being so cheaply available that the people would be unable to craft ammunition at home.

Not really. In any real civil war, some police forces would side with the rebels. That's already happened in connection with Public Lands issues in the Southwest. Also, at least some National Guard armories would be liberated. It could get very messy.