Gunpowder is the easiest part. The casing will be the hardest as you need pretty tight tolerances, but anyone who cares could have 50 trash cans full of cases in a week for a lifetime of reloading.
And if you don’t have cases for reloading, you can always use a case less design, then it’s just a matter of sourcing the projectile.
Of course there is always black powder, ball and cap, etc.