Good questions. I can give you the big picture but not all the details.
As far as I know, all the different mutant genes originated spontaneously out in the wild, in Africa. A germ cell mutation is a change in a gene's DNA in a cell that eventually produces a sperm or egg. Spontaneous is a fancy word meaning that we have no clue why the change took place; it just happened. Mutations also take place in cells outside the ovaries and testes, but only a mutation in a germ cell line can be passed on to the next generation.
Mutations can turn up in a captive bred group of animals, too. It's just that there are a lot more ball pythons over in Africa than in captivity, and people have only been breeding ball pythons for around 15 years or so.
It's fairly easy to create your own morph from combinations of mutant genes that already exist. Of course, once others learn what the combination is, they can do the same.
It is possible to mutate a gene in a lab. X-rays, various chemicals, and radioactive minerals are the most common ways to produce mutations in the lab. But the process is prohibitively time consuming and expensive to use with a slow-reproducing creature like a ball python. And there is no guarantee that such new mutant genes would be worth anything in the pet trade. So as far as I know, nobody is trying it, yet.
Hope this helps.
Paul Hollander