Is there any spot apart from the ziggurat where you can find metallo?
Nope, otherwise it’s the occasional regular egg
Its not that easy to find 
It’s terrible for me, 3 azid runs. None.
I have found him twice now, and I have ended up killing him in one shot while trying to eliminate the other arks first. :( But I am still searching for my third. Hopefully this time I will have a chance to catch him.