how do i get it???

The Electorizer is held by wild Elekids. (5% chance they are holding one)
To get a wild Elekid you need to have Pokemon Fire Red in you DS's GBA game slot and then go to Valley Windworks and look in the grass.

You can find Dawn Stones in Mt. Oronet and with the pickup ability.
Some Pokemon that have the pickup ability are Phanpy, Zigzagoon. I can't think of any others.

You are able to find an Electirizer by inserting Pokemon Fire Red into your GBA slot on your DS. If you have a DSi, you are unable to get an Electirizer unless you obtain Pokemon Battle Revolution and get one and send it via Mystery Gift. If you choose to insert your FireRed into your DS, you need to go into the grass of the Valley Windworks. Elekids are rather rare from my experience, and finding an Electirizer on one can be somewhat of a pain, so you should obtain a Banette, or another Pokemon with the ability Frisk. Send it out first, then it'll tell you if the Elekid you have found has an Electirizer. This saves a lot of time, and you do not have to capture several of them. Dawn Stones are able to be found in the first floor of Mt. Coronet, upon entry from Oreburgh or Hearthome City. You need to obtain the 5th badge, and gotten HM05, which is Surf.