Currently only the ashcan version released at GenCon is available. Only 250 copies of the ashcan were printed. A full distribution copy with final art, index, and corrections was planned but has not been released.
From the book:
The first Cthulhu Dark Ages was a success, spawning several monographs. Unfortunately, it never received official support in the form of released-to-distribution books. Rather than reprint the original Cthulhu Dark Ages, Chaosium decided to produce an updated version, with an increased page count. Andi and I were handed the task of building upon Stephane’s original masterpiece. As a fan of the first edition, and somebody with an advanced degree in 10th century history, I was thrilled. Deciding how to update it and increase its value as a game proved a monumental challenge. One of the most important changes is that the new Cthulhu Dark Ages is a supplement, not a standalone product. While most of the rules you need to play are contained within, the book does reference some spells and creatures from the core Call of Cthulhu rulebook.
As you read through the book, you will undoubtedly see many changes. Some changes were minor. First and foremost, Cthulhu Dark Ages has been updated for the 7th edition of Call of Cthulhu. There are some changes to the combat system to make it more deadly, a new, optional Sanity mechanic to better situate the rules within the early medieval mindset, and rules for the oral tradition—something to take the place of Mythos tomes in an illiterate world.
Some other changes are more grandiose in scope. The original Cthulhu Dark Ages was a toolkit but lacked a defined world for players and their Keeper to tackle. There were hints of the Dark Ages world here and there, but nothing to tell the players what made the Dark Ages unique and different from the High Middle Ages or the ancient world. Now, there’s the village of Totburh, a fully developed Anglo-Saxon burh (fortified dwelling) nestled snuggly within the Severn Valley; filled with interesting characters and more plot hooks than a Keeper can shake a shoggoth at. Granted, not everybody is going to be excited by Anglo-Saxon England, so there’s also a player’s guide to life in the Dark Ages that explains many of the concepts that were fairly widespread, but by no means universal, across the continent during the 10th century, which aims to illustrate exactly how alien the 10th century can be to modern players.