Onix - Pokedex Guide - IGN

Onix - Pokemon Diamond, Pearl and Platinum Guide - IGN

Pokemon Renegade Platinum First Gym, Onix Swept : r/nuzlocke

How To Evolve Onix Into Steelix In Pokemon Black 2 & White 2

Pokémon Platinum, Chuggaaconroy Wiki

Stunix #420.95 - FusionDex

Pokémon Adventures: Diamond and Pearl/Platinum, Vol. 8, Book by Hidenori Kusaka, Satoshi Yamamoto, Official Publisher Page

Crystal Onix [Pokemon Brilliant Diamond and Shining Pearl] [Mods]

Following the Trend, here's every Pokemon you can get in Pokemon Platinum before the first gym. : r/pokemon

Research - How many Pokemon are obtainable in each title?

Oreburgh Mine - Bulbapedia, the community-driven Pokémon encyclopedia