Can you get an Electirizer in Pokemon FireRed

No. Because Electivire was not made yet there is nothing you use to get it.
Answer No. The Electirizer is only obtainable in Pokemon Diamond or Pearl. It is equiped to some wild Elekid and can be traded with an Electabuzz to evolve it into an Electrivire. The item was not created until Pokemon Diamond and Pearl and hence would not appear in any previous Pokemon RP game.