Repairing shift interlock switch

My '99 Camry refused to move gear shift from "P" position. After a little research I was able to make it move using shift lock override button, but apaprently something is broken. I learned that it could be either brake lights, or some shift interlock switch next to the gear shift lever. Since the lights are OK, I guess it is that switch...

Does anybody know:
a) how difficult is it to replace it?
b) where can I get a replacement switch and what should I ask for?
c) is this procedure described in repair or service manuals?

THanks a lot in advance,
msr2k

There is a green wire with a white stripe from the brake light switch to the shift lock ECU.Toyota uses two different systems here.The Haynes manual gives an excellant check of these.