Yea I checked with dealer said not availabe!! It came out and locked engine up, I have it already to go except I need this part.You have talked to the dealer? i know you can get them for Kubota heads, i'd assume you could get them for a NH too.
Depending on how bad the crack(s) are, you may be able to use it still. I was told by a head machining shop that if they aren't right through, or close to right through they are still fine. If its a bad crack and the piece falls out, it will lock the engine up....