You don't really find Amped Toxtricity. Instead, you go to the Pokemon Day Care center, and the lady inside will give you a Toxel. The form depends on the nature of your Toxel. If your Toxel is:
then you will get an Amped Toxtricity.
Toxtricity cannot be found in the wild, but its pre-evo, Toxel, can.
Here are the places it can be found in:
Route 7, Bridge Field, Giant's Cap, Hammerlocke Hills, Motostoke Riverbank, Stony Wilderness
Here are the Max Raids it can be found in:
East Lake Axewell, Giant's Cap, Giant's Mirror, Hammerlocke Hills, Lake of Outrage, Motostoke Riverbank, North Lake Miloch