Hi, and welcome to the forums!

Getting company sponsorship is as simple as getting a job - it depends entirely on what line of work you're in and what the demand is for that type of work where you want to go. It also helps tremendously if you speak the local language, even just a little bit.

The easiest way to get to Japan (or any country) is to have the company you are currently working for transfer you. That way, they take care of the visas and generally pay for the move, etc. (If they don't have to pay for language lessons, they are much more inclined to consider transfering you, too, but usually there are language lessons in the deal if you need them and they need you there.)
Cheers,
Bev