How To Get DeepSeaTooth/DeepSeaScale in Pokémon Ruby/Sapphire/Emerald
Note: You must obtain HM 03 Surf and HM08 Dive to achieve the desired item.
The DeepSeaTooth is for Huntail.
The DeepSeaScale is for Gorebyss.
Catch a Clamperl and give either the Tooth or Scale and trade.