Where do you get onyx in fire red?

You cannot find Onyx in Pokemon FireRed. Onyx is a Generation I Pokemon and is not available in FireRed, which only features Pokemon from generations I and II.

However, you can find Onix in Pokemon LeafGreen, which has access to some Generation II Pokemon. You can find Onyx in the following locations:

* Route 24: Found in the tall grass.

* Route 25: Found in the tall grass.

* Route 40: Found in the tall grass.

* Route 42: Found in the tall grass.

* Rock Tunnel: Found in the tunnel.

Remember that Onyx is a Rock-type Pokemon, so you'll need to use a Pokemon with an advantage over Rock-type Pokemon, such as Fighting, Ground, Water, Grass, or Steel-type Pokemon, to catch it.