You should be able to fish and catch a poliwag, that will evolve to a poliwhirl at level 25. Bulbapedia says that Poliwhirls can be caught at:
Routes 22, 28, 30, 31, and 44, Ecruteak City, Violet City, Mt. Silver, and Viridian City (Surfing)
you will have the best luck fishing or surfing
you can catch a poliwag and evolve it into poliwhirl, and then use a water stone to evolve the poliwhirl into a poliwrath
you must trade with gold or silver in order for poliwhirl to evolve. kings rock
In Pokemon Gold, Silver, and Crystal, Poliwhirl evolves into a Poliwrath when you use a Water Stone on it. Poliwhirl can also evolve into Politoed if you give it a King's Rock to hold and trade it to another player.
Poliwag evolves into Poliwhirl at level 25 in Pokemon Liquid Crystal.
poliwag evolves at leve 25 into poliwhirl..veronica
eevee into vaporeon poliwhirl into poliwrath staryu into starmie shelder into cloyster
You'll need to trade for it or trade for a Poliwhirl that is holding a King's Rock.
To evolve Poliwhirl into Politoed in Pokémon Liquid Crystal, you need to trade Poliwhirl while it is holding a King’s Rock. First, obtain a King’s Rock, which can be found in various locations or received as an item. Once Poliwhirl is holding the King’s Rock, trade it with another player, and it will evolve into Politoed.
Make Poliwhirl hold a King's Rock and trade it to someone else, then trade back
Polywag evolved into Poliwhirl at level 25, an then into Poliwrath with a Water Stone.
Poliwhirl can be found surfing in these regions: Route 225, 227, and 228 after you get the National Dex.
If you get a Poliwhirl. Get a Water Stone and use it on it.