Tiger Shark available for purchase (15,000 coins) once you max out level 10 of Hammerhead Shark.
See the Mission 4 Map below for the eight shell locations (They said there are more than eight but I won't bother find them all) . Each of the mission requirements must be met in a single run. The use of revives (gems) are ok. Do not use a revive unless you are close to complete a mission.
Tiger Shark - Mission 4:
1. Angler Attack: Eat 10 angler fish
2. High Jump: Jump 8 meters out of the water
3. Jetlag: Eat 3 jet skiers
4. Kempy Kill: Find and eat the mythical Kempybass
5. Mass Murder: Eat 30 people
6. Survival King: Survive for 10 minutes
7. 5 Sunken Objects: Find 5 sunken objects
8. Depth Charge Swim: 250 meters below sea level
9. Super Mission 4: Score over 200,000 points.
Mission 4 Map with treasure location (red is shark spawn location, blue are shell locations) - courtesy of @QuickMythril. I was lazy to edit the original map with only shell locations