Once established, you can often get imports started on ordinary rats or mice. ASFs are 'African Soft-Furred Rats'. They're actually not rats, but are related to mice and rats. They're also called natal rats, and multi-mammate mice, because they have a tremendous number of teats--they can have up to 18 of them, but individuals may have more or less than that, and often have an odd number. These rodents are native to Africa, so would occasionally show up on the menu for wild ball pythons. As a result, wild-caught ball pythons may be more inclined to eat them.
They occasionally encourage fussy eaters to start eating again too, but then, mice and gerbils also sometimes accomplish that. Some folks swear by ASFs for ball pythons.
Imported hatchling balls should be started on fuzzy rats or mice just like CBB balls, because it's unlikely they were even fed before they were shipped to the US.
The good news on ASFs--they're extremely prolific, though a bit slow-growing, and they're halfway between the size of a mouse and a rat, making adult ASFs a good size for ball pythons. They purportedly don't have as bad of an odor as mice.
The bad news on ASFs--they're wild animals. They're not domesticated. Thus, without careful attention to taming, they will bite the bejesus out of you. They will also chew industriously through plastic bins, so it's recommended to keep them in metal. Strong metal.
I think ASFs are still pretty expensive. 30 bucks apiece? Feel free to correct me if I'm wrong, been a while since I checked.