The Armored Brown Bear mount is sold by Mei Francis with no requirements to purchase except the 750g base cost (which is reduced by reputation with the Kirin Tor). This is available to both Horde and Alliance players.
Mei Francis can be found within both versions of Dalaran, the first Dalaran is located above Crystalsong Forest. There is a portal to this Dalaran within your portal room in Orgrimmar or Stormwind.
The second place to find Mei Francis is in the Legion Dalaran in Broken Isles, you can reach this via your Dalaran Hearthstone.
Once in either of the Dalarans, you’ll find Mei Francis just outside of the pet store on the North/East side of Dalaran. Speak to her to purchase your mount.