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Swinub can learn it as an egg move or through a move tutor.
Same applies to Piloswine, but it also learns the move at level 0. To re-learn the move, go in the house to the left of the PokeMart in Blackthorn and talk to the fat dude. If you bring him a Heart Scale (which can be found as hidden items, by smashing rocks in Cianwood, or on wild Luvdisc), he will re-teach your Pokemon a move.