Can I apply for a 3-month Non-B visa in Bangkok while on a tourist visa?

:)

Not every company will do the in country conversions and some insist on sending people to a thai consulate to get the Non-B.

The only place around here that issues year-long, multi-entry Non-B visas (the kind you exit/re-enter the country on every 90 days) is the thai consulate in Penang

You need at least 15 days left on your current "admitted until" stamp to do it in country because of the 14 day under consideration period

You would take documentation from the company you're gonna work for and go apply for a 90 day Non-B at the immigration office. It goes under consideration for 14 days and then you go back and get the Non-B and the new 90 day stamp inked into your passport. Once you have 45 days or less left on that 90 day stamp, you take more documentation from the place you work for back to the immigration office and apply for a yearly extension of stay.