If you can't afford to buy one - have a go at making one from an old billhook. I saw someone using one he'd made for roughing out spoons with.
The one I saw was a Suffolk or Hertfordshire type with a convex blade. It also had a socket rather than a tang.
Cut and grind off the 'beak' and weld on a ring or hook.
I think the handle should be solid metal rather than wood - on the one I saw it just had a crowbar jammed in the socket.
Someone on the Bodger's Forum mentioned possibly adapting a drawknife?