(For the island players)Go to snow biome and find one between level 130-150(on console)or a 160-180.Pick it up to with a argy or something that can pick it up.Take it to the beach south of the snow biome.Grab yor longneck and a couple of tranq darts and knock it out.Put a couple of beries in it or vegetables.Wait for it to tame up and there you go your new megaloceros.

I did this with a blue event coloured one.

(^ for other help.)

More Megaloceros Taming & KO Tips