Here's some photos from my articles in "More Woodturning" on how I make crown blocks:

Here are some examples of what I've made for my wife - some have been in use for over four years:

Crown blocks with or without three hole mounting and with or without string grooves, to your specified height and size:

Crown 'stretcher' blocks with flange string groove bases:

Crown blocks with options listed above and with one or more sections to adjust height:

One and two sided brim blocks with mounting holes and string grooves:

"Dump" brim blocks (for turned up brims), with our without legs, centered or off-center hole to your crown block size, even or slanted string groove:

Finally, here's a ribbon shaper, priced at $40, that I can make to the size you prefer (my wife's is 14" in diameter):