Sarcosuchus can be found anywhere on the beach or the swamps.

Do not EVER attempt to knock out in the water. Sarcos are extremely quick and circle around you, making it difficult to get a hit in.

On land you can hit one with Tranq Arrows (take a number depending on the Level and your aim). Feed Sarcos fish meat for better results. Force-feed Narcotics or Biotoxin to keep their Tumor high.

It will take a bit of time, but taming a Sarcosuchus is in fact quite easy if your at least Level 21 and/or have access to Tranq Arrows. If you're using a Slingshot, find a Level 1 Sarco or good luck...