We haven't had any submissions yet, so I thought to tide things over until things pick up (this being a really young blog, and all) I'd share with you some of my favorite suppliers! Let's start with Hat Shapers.
First, you should really read Hat Shapers' Note to Professional Milliners. These are not intended for professional use, but if you're just looking to make hats for yourself and for costume use, with a little creativity they ought to work fine.
One of the biggest impediments to aspiring hat-making hobbyists is the expense of hat blocks. Traditional wooden hat blocks are very expensive, which is quite an upfront expense for hobbyists. Hat shapers are plastic hat blocks, and most styles are only $28 each! Most styles come in multiple sizes (they are made from wooden blocks, so some styles (especially the children's styles and more unusual shapes) are only available in one size or in very limited sizes). For a small extra fee, some styles can have brims added (they look like they have brims, but the flat bases are only intended as a stabilizer for the body of the hat block).