Brock's Rhyhorn has Horn Drill, and it's level 41, but it's pretty tough to get a slightly-higher-level Smeargle to survive its other moves before it actually gets to using that one. (Remember, Fissure, Horn Drill, and Guillotine have exactly 0% accuracy in this game if the opponent has a higher level than the user, so you don't have to rely on luck if the level spread is set up correctly.)
Cooltrainer Gaven on route 26 is a rematchable trainer who brings a team of Victreebel, Flareon, and Kingler, and the Kingler of course has Guillotine if you want to try and sketch that after it gets used. (Beware because Kingler also has Protect; if you try to click Sketch the turn after you see a Guillotine, he could use that and you'll end up sketching Protect instead.) Kingler starts out at level 32 and gets as high as 38 in the rematches, if you want to make sure Smeargle has the correct level before trying that.