TM100 does not exist in the Sinnoh games, so it is impossible to find a TM100. TMs stopped at TM92 (Trick Room) in those games. I guess if you count TMs and HMs together then Rock Climb would be TM100, so in case that's what you meant you can find Rock Climb in Route 217.
There is upto TM 92 Trick Room but there is no TM 100. There are 8 HMs too.