Caleb Adding to what Gabi was saying, the first two books were released in hardcover for the first time ever recently and can be bought on most online bookstore retailers. The last two, due to publishing switch-ups and a massively successful Kickstarter campaign, were released in hardcover with original cover design a few years ago and you'd best look on eBay or some similar thing if you want to find one. But if you wait until September, books #3 and #4 will be rereleased with brand new hardcovers and illustrations. Hope this helps!
Gabi Looks like if you need it now, you'll have to look in 2nd hand bookstores, and they are rare. BUT hang in there for six months, because they are being re-released in hardcover on September 15th and 28th respectively.