Either its in cerulean cave or on Cinnabar island u need rock climb for cinnabar.
In cerulean cave
To evolve electricity into electivire via trading, you must hold the electrizer.
mt mortar
You have to trade it with an Electrizer on it.
Get an Electabuzz, give it the Electrizer, then trade it
Trade your Electabuzz holding a magnet.
Electabuzz > trade with electrizer > Electivire
You can find the Electrizer in Cerulean Cave after you defeat all sixteen gyms and battle the elite four for a second time.
It is a thing that you give Electabuzz so when you trade it it evolves into Electivire.
U cant find electivire out as a wild pokemon...u must find the item electrizer and catch an electabuzz. Then put the electrizer in to electabuzz and trade it...
You can find an Elictrizer in Cerulean Cave. Its deaply within so be prepeared!
You cant, You can only get The "Magmarizer"Unfortunately, the only way to find an electrizer in Soul Silver is if you use the Pokewalker. I don't know the route or the number of steps to get it, but if you go on seribii.net then you can find out.