Garrison Hearthstone
Source: Quest. If you lost your stone you can ask (Alliance) or (Horde) to squeeze another one for you, free of charge.
The 
Garrison Hearthstone is a quest reward from Draenor that teleports you directly to your Garrison.
Guide awaiting review
Travel to Frostfire Ridge
Horde players who skipped Draenor via a character boost should take the portal from Orgrimmar to Ashran, then fly from Ashran to the Garrison location in Frostfire Ridge.
Find Thrall at the Ship
Since no Garrison exists yet, descend east of the Garrison location to the original Frostfire Ridge landing site, go down to the beached ship, and pick up the quest from Thrall.
Complete the Starting Quests
Progress through a handful of quests, including killing the large gronnling boss and watching the Garrison be constructed — the quest that completes this chain awards the Garrison Hearthstone.
Replace a Lost Hearthstone
If you lose your Garrison Hearthstone, Alliance players can speak to Deedree and Horde players can speak to Provisioner Rashma to receive a free replacement.
Tips
Bubble Hearth works with the Garrison Hearthstone.
You can combine the
Garrison Hearthstone, 
The Innkeeper's Daughter, and 
Dalaran Hearthstone into a single macro using /use on each, triggered by left click, right click, and mouse wheel click respectively.
