After you fix the machine on 1 Island with the ruby and sapphire, it allows you to trade with the games emerald, ruby and sapphire. You can trade a Treeko from one of those games to FireRed.
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Yes, but only by obtaining the National Dex and having a friend trade his/her Treecko.
you can get treecko by shacking the trees on ilex forest
migrate
In Pokemon firered you can't, but in Pokemon leafgreen you can get it then trade it to Pokemon firered.
Ruby, Sapphire and Emerald.