Amazon shuffles the products between warehouses sometimes, and they list the items as “backordered” while they are in transit and unavailable for immediate purchase. They will show up as “available” when they’ve reached their new warehouse. Normally this kind of stuff isn’t apparent if there’s sufficient stock of the items, but it’ll show up at times like this when there are only 2 of the starter kits left.
Protoshields have been shipped to Amazon and should appear online maybe this weekend. I’ll try to get some more boards and kits to Amazon, but I’ve been out of the office most of the past month with travel and field work, since this is the prime season for deploying dataloggers and stream sensors.