I found one down at green ob river ( island ) and one up in the snow, tip, kill all reindeers around because they look like sheep from a distance. I also found one at an oasis in the desert and on red on mountain ( scorched ) and as for center I found them in the snow on top of mountains around green ob. Hope it helps...
Easy place to find in Fjordur is Jotunheim, go SouthEast. The cold there is killer but the best way to stay alive I've found is with full fur gear, an otter around your neck, Frio curry soup to keep help with the insulation and med brews as well as blood packs on your quick slots. I recommend at least bringing 20 or more med brews if you plan to stay alive longer than 2 min.. a HOT tek canteen will work wonders if you have one.
Use a desmodus(Bat).
WATCH OUT for microraptors and other predators!!!!
OVIS are an instant passive tame with sweet vegetable cake!
The frist time I saw mine, I was on the edge of the redwood forest near a small stream. I picked it up with my Argent, so if you want to take it home and save it for breeding or tame meat that's the way too go.
I was searching for these guys for the longest time on the island, gave up on it and went about my taming business. Build a trap over the river from my tree base, fly to the local mountain, grab a parasaur and start leading the female giga to my trap. It gets the parasaur, so I grabbed the next closest grabbable creature. An ovis. Now. Really game?! Rip to the sheep that baited the giga the rest of the way through the valley :(