You get it from Captain Stern in Slateport City after finding the Scanner in the Abandoned Ship but you need a Pokemon with Dive.
EDIT:
You can get BOTH that is to use GameShark
The steps...
1.Go to YouTube and type this in the search box,Pokemon Emerald-ALL ITEM on sale!!! (you can just copy and paste from here.The user is smarkoh)
2.Go click on (more info) at the description and the cheat is available there.
3.Pls rate and comment.
***The cheat is for ALL(most) of the items and it only works for emerald
No only in ruby and sapphire and emerald.
deepsea tooth gets you huntail while deepsea scale gets you gorebyss. You can decide which on you think is better now.
Go to route 221 and fish for a Clamperl. Make it hold Deepsea Scale and trade it. Deepsea Scale can be obtained by catching wild Chinchou. They sometimes hold it.
It requires a deepsea tooth or a deepsea scale.Once the either item is obtained, and attached to clamperl, clamperl must be traded to another pokemon cartridge. The deepsea tooth helps it become huntail, the deepsea scale makes it evolve into Gorebyss.
in fact it does not evolve with leveling up. It evolves with a deepsea tooth or deepsea scale held via trade. Glad if I could help.
First you need to go through the abandoned ship and get a scanner from a scientist in there Note: need dive, then give the scanner to captain stern and he will allow you to choose either a deepsea scale or deepsea tooth obviously you want the tooth. Finally have a clamperl hold the deepsea tooth then trade it to a friend then take it back and it will be huntail, if you chose the scale you will get gorebyss instead of huntail.
Both can be found in White Forest and Join Avenue.
to get a heart dive
in one room on the abondoned ship, you can dive, then you have to enter rooms and find keys, eventually you will get the scanner in RM. 2. Take it to Cpt. Stern, and he gives you a deepsea tooth or scale. They evolve clampearl through trade into huntail or Gorebyss
The Dragonscale is an item in Pokemon Emerald version. There is a chance that certain Pokemon such a Horsea will be holding one when you catch it.
On wild Pokemon and serval locations.
It's a pink eel pokemon. It has a beak and looks like a female pokemon, it is pink and has banner looking things attached. You get it when you trade a clamperl with a deepsea scale attached.