You can even cast both musket and minié balls over a campfire, and sharps rifles worked great with paper cartridges. Add to it that gunpowder was widely available in wholesale quantities at the time, and it would have been almost trivially easy for him to keep his troops supplied with ammo.
It existed in the world. He could steal powder and balls and stuff from his enemies. Those bullets would need to be made somewhere.
You can even cast both musket and minié balls over a campfire, and sharps rifles worked great with paper cartridges. Add to it that gunpowder was widely available in wholesale quantities at the time, and it would have been almost trivially easy for him to keep his troops supplied with ammo.
And with the bigger guns it would be extremely easy for him and his newly freed friends to go and get the stuff.