u/AtomicMatrix

This workaround is for those who can't find any black bears due to story progression or locked out. To get the black bear as a mount, you'll have to get the brown bear to break open the black bear's steel enclosure, which you can't do yourself. It's best to use Kliff for this task as his Force Palm is the easiest to do. Equip the Health Detection Device headgear if you have it as that'll allow you to see the bear's health status.(See the 3 images I've posted for location and the types of enclosures of each bear is kept in)

1. Go to the location on the map(see image), which is Rocca's Hill Slave Camp.
2. Head to the very top part of this camp where you'll find a black and brown bear. The black bear is in a steel enclosure and the brown bear is in a wooden enclosure(see images).
3. Smash/break the brown bear's wooden enclosure. Once the brown bear is out, lure it to attack you by positioning yourself behind the black bear, and in turn will break the black bear's steel enclosure.(The NPC's loitering around the cages will all be gone when the bear is out, so don't worry about them attacking the bears lol)
4. Once both bears are out of their respective enclosures, kill the brown bear, but be careful not do too much damage to black bear or accidentally kill it in the process lol. If the brown bear decides to run away, even better for you.
5. After dispatching the brown bear, force palm the black bear about 3 times in a row and you'll stun it. When you can see the "Ride" prompt pop up, jump on it and feed it to 100% and you've got your black bear mount.

Black Bear Enclosure

Brown Bear Enclosure

Rocca's Hill Slave Camp