Lapras is a water type of Pokémon which is used by Ash in the Pokémon anime. It is not possible to find one in Ruby. The only way to get one is to trade.
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I don't think it's possible, you can only get a lapras in the Kanto region... I was wondering the same question until I came to this solution.
you need a cheat that can catch a trainer's Pokemon to have lapras. because there is a trainer that has a lapras.
you find lapras in union cave B2 only on fridays
Union Cave
I don't think you can but if you have an Action Replay you could catch the trainers lapras.