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.
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mt mortar
Get an Electabuzz, give it the Electrizer, then trade it
You can find the Electrizer in Cerulean Cave after you defeat all sixteen gyms and battle the elite four for a second time.
You can find an Elictrizer in Cerulean Cave. Its deaply within so be prepeared!
put in Pokemon fire red and there will be a elekid with an electrizer in the valley wind works field.