According to the ingame Pokedex, it can be found at the Viridian Forest, however I cannot find one from the usual methods (tall grass, headbutt trees, etc.)
How exactly can I find one, or can I find one elsewhere?
Remember that they are limeted in Viridian Forest. And, sorry to say this, but that is the only place to find a wild one. Unless you want to trade with someone. Oh, don't bother using honey or Hoenn sound, use Headbutt, they only live in the trees.