They are in all biomes, they just goe really really fast o_o I had luck and managed to grab two more and one miss click which I think I'm going to bite (edit: Of course the egg died). It seems to be bit easier to grab them now than last evening.
I hope it's not a joke, they look amazing!
And here's the eggs description: This translucent egg shines like starlight.
Edit: They seem to be real release.