No, Mewtwo cannot be caught in Route 224 unless an Action Replay was used. The only legitimate way in getting Mewtwo in Pokemon Platinum is by migrating it from Pokemon FireRed or LeafGreen to the Pal Park.
You can't access Route 224 until professor Oak upgrades your Pokemon. Then go east of Victory Road. Route 224 is the eastmost Route in Diamond Pearl and Platinum.
lapras
You can get him/her on route 224
First, go to the Pokemon Leauge.Then, right above the Pokemon League is route 224
route 224
route 224. {flower paridise}
You can find them if you fish in route 224.
Route 224 Poke Radar
route 224 affter getting the nasinal pokedex
the flower paradise on route 224
Route 222 or 224.
They swarm occasionally on route 224