Impossible
You can catch Ditto at route 218. Ditto around there are usually lv 30. :)
You can catch a Ditto in Pokemon Diamond after you obtain the National Dex and use the Poke Radar in the grass in route 228(or 227). Dittos have appear about 20% of the time.
On Land
Ditto can be caught on Route 218 (east of Canalave City) with the Poke Radar. It is rare, however.
The only way to catch a ditto is with a pokeradar. The only other way is through trading.
you can catch dittos in Pokemon diamond and pearl with poke radar in route 218 but its pretty hard to catch them + find them. :)
There are 12 starter babies in the Pokemon World To Get Bulbasaur Catch Ivysaur and a Ditto To Get Charmander Catch Charmeleon and a Ditto To Get Squirtle Catch Wartortle and a Ditto To Get Chikorita Catch Bayleef and a Ditto To Get Cyndaquil Catch Quilava and a Ditto To Get Totodile Catch Croconaw and a Ditto To Get Treecko Catch Grovyle and a Ditto To Get Torchic Catch Combusken and a Ditto To Get Mudkip Catch Marshtomp and a Ditto To Get Turtwig Catch Grotle and a Ditto To Get Chimchar Catch Monferno and a Ditto To Get Piplup Catch Prinplup and a Ditto
You must use the PokeRadar on Route 218. They are kinda rare though.
The only way I know of getting a Ditto is to migrate it from one of the GBA games and then catch it at Pal Park.
go to canalave city go then walk to route 218 use the pokeradar it will take awile. then throw a ball at wala you have a ditto
i have Pokemon diamond, and played 600 hours. its not possible. but you can catch a ditto, and make Pokemon eggs.
Ditto* you can't get one there You either trade it online Or transfer it from firered or leafgreen to the palpark and then catch it.