You can catch a Sneasel in the Underground with Throat Chop, or catch a male Smeargle, a female Sneasel, and a Heracross. If you choose the Heracross Method, level Heracross up to Level 40, where it learns Throat Chop, and then go into a Double Battle with Smeargle and Heracross in the front of your party. Sketch Throat Chop from Heracross, and then breed the Smeargle with the Sneasel to get the Pokemon you want.
Hope I could help