You can catch it in Slowpoke Well. That's the only location I can remember.
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You can catch Slowpoke in Pokemon Gold in the Slowpoke Well that is by Azalea Town and you can also find them in Tohjo Falls.
Have your Slowpoke hold a King's Rock, then trade it with a friend to get a Slowking.
Unfortunately, you can't. ~MoNgOoSe
I think you have to level it up to Level: 34 hope this helps
You have to use the PokeRadar on Route 205