This is an interesting video interview with Lorenzo Ray. A block maker in France.The article is a bit dramatic as it suggests that Lorenzo is one of the last 4 block makers in the world. This is overstated.
This video demonstrates a use of hat blocks to make a buckram form which is then covered with fabric to complete the eclectic top hat.
Informative video with Victor Osborne shows how to make a hat crown form with expandable foam for the do-it-yourself hat block.
A PDF presentation showing various hat block styles and shapes.