I took mine out to paint it. There are two small screws in the front. After removing those, you can technically pop the circuit board out. But, be careful, I cracked mine. The correct way to do it is to remove the AC control unit (the entire white piece). On the bottom, there are a few more screws. Remove those and the circuit board would just pop out easily. This would be a heck of a lot more work, of course.
Toyota does not sell the little bulbs by itself. You might have to buy the entire circuit board. ($55). I went to 5 different dealers in So Cal and they all told me the same thing.
I went on eBay and bought one off of a wrecked Celica for $20.