I recently wrote to GreenBrier Games and asked about a second printing. This was their reply:
Thanks for reaching out! You're right, Grimslingers is entirely out of stock everywhere - we ran out of the first print run within only a few weeks of its release. So we fired off the 2nd print run right away, and our manufacturer is doing everything in their power to make it a speedy turn around. Our estimate is that it will be in stores early December. Unfortunately just after black Friday, but hopefully still in time for Christmas sales.
At which point it will also be on sale on our webstore, if you can't find it at a local shop.