Yes, but it is very tricky. You will need a PokeRadar, which the Professor gives to you after you beat then Sinnoh Pokedex.
Then, from there, fly to Canalve City and go to the tall patches of grass. Use the PokeRadar and go into the shaking bushes until Ditto appears. He is very tricky to catch, though, so you need some good Pokeballs. I would suggest getting a few Master Balls from a friend with cheats.
~Lucario
Chat with our AI personalities
You can find it at random days in Pokemon Mansion in route ---, talk to Butler (or whatsoever) and he will say random Pokemon is in the garden, if is ditto, go get it!
how to get a togepi in Pokemon platinum
There is no grunt that you can give a Pokemon to in Pokemon platinum.
That pokemon is Azumarill in pokemon platinum in the national pokedex
No, you cannot get Jirachi in Pokemon platinum.