I've been playing on teams with them all week. They seem like a lot of fun. I wish I could help, but I haven't unlocked him either =(
Have you tried asking someone that has him in one of your games or possibly the battle.net forums?
Edited: I just noticed the disclaimer about Cho'gall
Note: During the Cho’gall Buddy Brawl event, you can obtain Cho’gall by completing the quest, random seeding at the start of the event, or a BlizzCon loot code. After the event, you will be able to purchase Cho’gall from the in-game store.
So you might be able to group with a friend and play a bunch of random games until you get him =)
» Edited on: 2015-11-27 05:22:00