hi, I live in bogor, 50km south of jakarta.
have no worries!
in indonesia, I believe there are more mtb's than roadbikes.
professional workshops are plenty.
parts shops have the most expensive items you can imagine.
and trails?
hmmm. never worry.
just come to indonesia and contact me at tkwardhana@yahoo.com
and I'll refer you to the experts.
(by the way, I am not a mountainbiker, I just commute on asphalt, on my hybridbike)