The Lost Island Map in Ark Survival Evolved has a neat little cave where the Magmasaurs have their nests. It isn't too hard to get the eggs if you take your time. You can lure the magmasaurs out of the cave by grabbing an egg and running or flying for it. If you don't get blasted by their fire you will have the cave to yourself. On my single player Lost Island map, I had three nests with four magmasaur eggs. I got level, 20, 85, 85, and a great 145 egg. That is probably the only magmasaur I will need. Don't forget to eat the low level eggs, so new eggs will spawn in.
They have updated the coordinates on the map, the coords below are accurate.
Magmasaur egg cave locations
Lat 23.4 Long 64.2
Lat 19.0 Long 67.3