... from Crosmods. Pays for itself in no time. Here is mine:
It has a Mountain Air valve and Cothran extended bolt probe. I lapped the barrel and recrowned it. The home grown shroud was replaced with a TKO and it is very tame now. Scope riser was an ebay find and is a necessity since the Crosmods adapter is not angled like the original.
I can't pry it away from my 12 year old so I have been casually looking for another. Broke down and bought a p-rod this weekend and plan on carving a carbine stock for it as my replacement.