I just tried to buy Speer or Hornady soft lead roundball .454" (44 cal cap and ball).
Tried at : Natchez, Midway, Cabelas, Basspro, Dixie, Track of Wolf, and two or three ammunition online shops.
All were out.
I think the shortage of guns and ammo nationwide is spilling over to the cap and ball area. I would guess folks are buying a .44 cap and ball as a last resort, pending new gun laws. And then they need ball. And hence the shortage.
Both brands out of stock seemingly almost everywhere (in that size). Including local brick and mortars around here.
I went to gunbroker dot com and grabbed some at auction.
I do believer other sizes might become rare too.
The safest way is to have a mold in the size you need for home casting.