Where do you get a lickitung in pearl?

To get Lickitung in Pokemon Pearl you need the National Pokedex which you get for seeing every Pokemon in the Sinnoh Pokdex. After getting the National Pokedex talk to your rival's sister in Sandgem Town until she says Lickitung have started appearing in Acuity Lackfront. Go to Acuity Lakefront and a Lickitung should eventually appear.