Weezing is a Gen 1 Pokémon and only appears in the original Kanto region. It can be found in the following locations:
* Route 22: During the day, with a 5% encounter rate
* Route 23: During the day, with a 5% encounter rate
* Route 24: During the day, with a 5% encounter rate
* Power Plant: During the day, with a 5% encounter rate
If you're playing Pokémon Diamond or Pearl, you'll need to trade with someone who has caught a Weezing from the Kanto region to obtain one for your team.