When hunting for eggs be sure to use a high level bloodstalker. a lower level is fine but riskier. use it to get past the cave critters and in the back of the cave is a cliff that overlooks the nests that is safe. use the glide parachute function to get over the nest and once all magmasaurs are away or led away you can quickly jump down and grab the egg. once grabbed get back on bloodstalker and double jump straight up and aim for the ceiling not the cliffs or you'll get glitched. once you're back on the safe cliff you can teleport out. beware of onyc when in the nests they can mess it all up. and at all costs avoid the mortor strike attack of the magmasaur, the bloodstalker cannot grapple while under burning effect.
for raising use air conditioners ranging 10 to 30 depending on biome and then use ankylosaurus to farm Ambergris on lunar biome before hand. keep it on a dino for max spoil travel time till you can get it to a fridge for the maximum preserve time and hatch the egg, enjoy!
I’ve found the eggs. The eggs are located inside the volcano in an amethyst cave. There are lava pools with groups of magmasaurs in them. There are small islands with craters in them, within those craters the eggs are nestled within. But be careful there are lots of magmasaurs, magma, and what look like varient rock elementals.