Tralok Eyes are acquired by cutting up Tralok caught through Fishing. Go to Fisher Hai-Luk in Cetus, select the desired amount of Tralok available, and select the "Cut Bait" option to extract the components. Each Tralok cut yields one Tralok Eyes.
Alternatively, Fisher Hai-Luk can sell Tralok Eyes in bundles of 20 among her rotating stock of "Daily Specials", which can be bought for Platinum.
Tusk Thumper can also drop them.