There is no 'Breeding Center' in any of the Pokemon games. However, you can breed two Pokemon in the Daycare, located south of Goldenrod City.
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You can only get it from breeding it from Jigglypuff or Wigglytuff
He only learns it via breeding but only in Pokémon HeartGold and Pokémon SoulSilver.
You can get a Munchlax by breeding it with Snorlax holding a Full Incense, or you could transfer it from the Poke Walker.
It is in Viridian City, behind the Poke Center.
in the route just south of goldenrod city