If your on mobile and can’t find one of these guys start the tame equus pursuit and walk or fly around the island and eventually a arrow will show up on the top left of your screen. If you follow that then you will find an equus or two. Upvoote if you found this helpful.
If your looking for these guys, I don't know if it's a guaranteed spawn but if you look around the rivers around the green obelisk, they seem to spawn to up to groups of three. I've tamed two from that same area, but be careful. That area has rexes, carnos, spinos, and allos, so bring something that can kill them. If you can't find any equus, just clear out the area. Also not about equus, but ovis can spawn here as well. I found two of them here in the jungle...
Put this higher !!So if you play mobile I found 3 in the same spot okay so first do the volcano pursuit the one where it's the cave inside the pursuit should be south of the equator and in that general area if you look around you'll find them
If hard to find on The Island, a herd seem to spawn near the red obelisk, green obelisk and the black sand area off the river next to the redwoods, I killed a bunch of low levels for some easy pelt and I came back after 10-15 minutes, after I found a 145 Equus. Hopefully you found this helpful.