Where can you find the electraliser in Pokemon Diamond?
You'll need the Pokemon FireRed GBA cartridge. If you have it,
go to the Valley Windworks and catch an Elekid; it has a chance of
holding the Electirizer.
Two suggestions:
1. Use Pokemon Pearl. In Diamond, the Elekid only has a 5%
chance of holding the electirizer, while that chance is 50% in
Pearl.
2. If you insist on using Diamond or don't have Pearl, use the
Poke Radar to get Elekid. Once you find one, catch it, and when the
battle scene ends, the poke radar animation will go again and the
grasses will shake. Proceed to the shaking grass furthest away from
you. It will have the same Pokemon you just caught or beat. This is
called a Pokeradar chain; its recorded by App 20 on your poketch.
Chain up Elekid till you're sure you've found an electirizer