when you go to the psydex and look at dittos location for d/p it says no location but you can use the poke radar to find ditto in route 218 near canalave city where there is only the one patch of grass.

http://www.psypokes.com/dex/psydex/132/location

Check the box, press Submit button, receive bacon...er...Ditto location. Same for every other Pokemon found by Pokeradar.