Can anyone explain to me exactly where you can get Nightmare Decks? I just recently found the Shadows of Mirkwood decks on eBay, but is there a place I can get the new decks as they come out in the future or is finding them online through places like eBay the only way currently?

The nightmare decks are first available from FFG in the form of Game Night Kits, these are tournament packages. But only retailers can order those, you can't get them normally. Ask your local game store if they can special order a kit for you. Mine allows me to do this so I get them before Ebay on most occasions (I currently have the latest nightmare decks, the later half of Shadows of Mirkwood cycle). Saves me time and hassle. Otherwise, Ebay is your answer for the most up-to-date nightmare decks, but expect to pay double the price. Once the kits are out of circulation, you can buy them individually as PoD from FFG and from other online or brick and motor retailers. They should be readily available at that point.