To pre-empt users here:
It’s not available this year / But it’s not linked to the achievement
" Return to Alterac Valley of Olde
Run down your enemies, raze their fortifications, and exchange the tokens you loot from their corpses to summon mighty reinforcements in Korrak’s Revenge, a throwback Battleground inspired by the earliest days of Alterac Valley.
Players who participate in Korrak’s Revenge and complete the Alterac Valley of Olde achievement can earn two mounts: the Stormpike Battle Ram (Alliance) and the Frostwolf Snarler (Horde)."
But blizz says check wowhead
Top wowhead comments from years past show its tied to the achievement
But ok, you need to check your progress on a single character in the PVP menu
Not even remotely showing any sort of progress
But ok, you still need to do it on one character
This guy did and didn’t receive the mount
It’s ok, though. Keep queuing up 20 minute waits for a slog of a pvp match that won’t give you the reward it’s supposed to.