Find a Smeargle on Route 7, and sketch something onto it.
This is normally if the Smeargle can survive the attack. For example, you can use Baton Pass on a Smeargle in Route 7 with no one else in your party, and then Smeargle can Sketch the Baton Pass, then you can catch it. So yeah, if your desired move can let your Smeargle survive, you can catch one on Route 7.
If that's not possible, catch an unsketched Smeargle and find the Pokemon that has your desired move. Save the game, and battle the Pokemon. You will need to continuously Sketch it until you get the move. This will be annoying, so I'd prefer the above method. Of course, there is a possibility the above method may be rather unreliable.
Breeding doesn't pass it down, ignore the whole thing I posted about breeding it. xD
Hope I helped. :)
Source and Experience