As I begin focusing production on the Standalone Controller, I have one Sentry Shield remaining in stock. This will be the last one sold for a while. As such, I will be selling it over here on eBay:
Bidding will close on the 28th.
For those who have not been able to buy a shield, there is a large batch of the standalone controllers coming in. I also encourage you to check out the options for wiring the sentry to your own Arduino without the Sentry Shield - it's fairly easy to do, just check out the Wiring section of the website.