I also found patchcraft growlers in Frostfang Sea on the main island at (approximately):
/way 300, 53, -260 (near the ferry dock / cove, on the ramp of the "false trail to Halas") /way 400, 43, -485 (near "The Deadly Icestorm" spawn point, between Grizzly cave and Pride Overlook) /way 65, 75, 275 (between the Rogue's guild and Cragged Spine)
A few additional notes, that might accidentally be helpful:
1. It may be wisest to pull it away from the spawn point a little. Another may spawn before the battle with the handler (who appears after the 2nd patchwork explodes into confetti) is done... or if you're taming, it may appear before you've named your new warder.
2. It seems to be completely random on which of the two color schemes you get, which may interest BL's that want to tame them. So if you don't like the color of the first one, you have a 50%-ish chance of getting the other color on the next one.
3. The /loc already posted for Grizzly Bear area ... it's on top of the cave, not inside it. ;-)