Where from?
I've done them for a few teams

What material?
Nylons typically work best. Either straight nylon or carbon fibre nylon such as onyx Best to not use them as slippage pulleys though as the heat generated melts the plastic.

What fill pattern?
Depends on the print tech

Where do you obtain the 3D files to send the printing people?
You can CAD model them yourself. Alternatively you get your 3D print provider to do it (yes I can model pulleys)

and can you edit them before sending?
If you have the CAD software to model them yeah