Breed eltabuzzs and hatch the egg
The Electrilizer is held by wild Elekids which can only be found on route 205 with Pokemon FireRed in the Gameboy Cartridge
The item "Electizer" is a held item that wild Elekids will sometimes hold. The probability that an Elekid is holding the item depends on which version of Pokemon you are playing. For Pokemon Diamond the probability is 50%, and in Pokemon Pearl the probability is 5%. You can catch wild Elekids on the south end of Route 204, or by the Valley Windworks if you have the game "FireRed" inserted into your DS as well.
Insert a FireRed cartridge into the gameboy and you can find elekids in route 208 and Valley Wind works (this process is called insertion. Can work for other Pokemon GBA games.)
Elekids normally hold it
Yes, it is hard to find a Elekid in Pokémon Diamond, because first of all you have to insert Pokémon FireRed. After that it is to be found at Route 205 - South and Valley Windworks with a Rarity of 8%.
You catch an elekid holding one. Doing the insertion technique with firered version, you can catch elekids outside of valley wind works. Elekids are hold an eleckitizer 50% of the time in Diamond, but only 5% of the time in Pearl
Catch a bunch of elekids and they sparingly hold them.
get firered and insert it into the GBA slot then go to the valley of wind works, the elekids in that grass patch will be holding one
wild elekids hold them but its only a 5% chance they will
Wild Elekids and Electivire's have a 5% chance of holding them when you catch them.
In Pokemon firered you can't, but in Pokemon leafgreen you can get it then trade it to Pokemon firered.
There is no Pokemon convention in firered.