I'd try milliput black for these. The other thing is the hats - milliput cures in about 2 hours, though becomes harder to use after 45 minutes (all depending on heat/humidity)
Initially it's like a clay, but it becomes increasingly plastic in character as it cures.
After maybe 20 minutes the stuff becomes very stable upon rolling, so you can use a felt tip pen to roll very thin sheets. Then cut the hat brims and use a cocktail stick wetted in warm water - will work a treat!