Set your spawn rate to max if it isn't already - that should improve the chances of a LongTooth showing up.
I found those beasts all over the place in the Enchanted Sea - including right next to Talrik (which was very handy indeed). Doesn't matter where you actually find the skin as long as you get it so go hunting for crab shells or anything else you may need to do in the E-Sea area and eventually a LongTooth will arrive!
Good luck!
Wyv
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