If you actually just need a replacement PS/2 cable, it looks like eBay has them for sale.

Monoprice sells PS/2 to USB dongles.

If you have little to no experience with programming at all, I suggest trying the assembly game TIS-100 first to wrap your head around the concepts, rather than trying to learn 6502 right away.

I would pair it with this tutorial, which is really just a bottom-up programming course.

Python is very different from assembly, but assembly isn’t hard to learn if you apply yourself and take it slow. It will seem kind of abstract without something like the game above to challenge your understanding.

How many chip collectors exist on the entire planet, I wonder?