Since I have made these before I have all the materials on hand. If you are just starting out you will need to get some felt rovings and sheets of felt for the scales. The rovings can be ordered online or purchased at some yarn stores and other craft stores. I buy mine at a local yarn shop where I can get it for 75 cents per 1/4 oz. It takes about 1/2 oz to make the main body, all other parts take less than a full 1/4 oz. The felt sheets can be purchased at a craft store for about 33 cents each. Wool felt is best but you will pay a premium for it. For the scales inexpensive synthetic felt will work.
Along with the materials you will need the tools for felting. These can also be purchased where you buy the rovings. Felting needles are the main thing. You can buy individual needles or special pen holders that hold 3 or more needles at a time. I recommend getting one of the 3 needle holders for anything of bulk. This makes the work go faster and the larger implement is less fatiguing on your hand. You can also remove two of the needles and use it for the detail work. Children also do better with the multi needle tool because it is very easy to break needles and the tool makes it easier to hold them straight. The needles can be purchased for a few dollars each and the 3 needle holder I have was $17. The only other thing you really need is something to felt on. I prefer foam, nice spongy dense stuff is best. Find this at craft stores or if your lucky for free as packing material. Some people use bristle brush like bases but I have not tried these yet.
General tools you will need include scissors and a razer blade. I also like Netflix, felting is one of those things easily done while watching a movie or TV show. Nothing too exciting where you need to be glued to the picture but something easy helps pass the time. I watched the West Wing while doing this and its perfect.