If you wish to find go to winters mouth, face the icebergs and head left around the beach. From the first icebergs to the ones you see after going around the beach, and a ways up the mountain. Not Ovis city but I got four in an hour. Never could find a female. I hope you have better luck than.
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 :(
I saw a comment asking where to find them on the Island, they spawn everywhere, especially in the icy mountains but I found one as far down as 3-4 island in the bottom of the map (the one with the cove). The reason they aren't seen often is so many things eat them, so you have to be quick to snag one for yourself
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.