To get a visa, first you need to find a company that is willing to hire you. Once you have that, the company will be responsible for supplying you a visa, so its not something you need to worry about personally.
If you're on a visa that allows residence in Japan, such as a student visa, you can change to a working visa. For changing from a tourist to working visa, it looks like the rules may have changed, hence the confusion to whether or not it is possible. Also note that immigration laws in Japan leave a lot of discretion to the person processing the application, so it is hard to get clear answers on what is and isn't permitted.
One thing to keep in mind though is that a tourist visa lasts three months, and it will often take a couple of months to process a working visa. If you don't receive your working visa before the tourist visa expires, you will need to leave the country.