First of all for future reference.... The sender must be instructed to remove the governor and place it in bubble wrap or similar protection. Also these engines must never be packed for shipment with foam peanuts as they are a recipe for disaster.
Finding governors for popcorn wagon engines is quite difficult.
Cretors are much more common and there have been castings for Cretors governors.
I have never seen an orphaned Dunbar governor and to my knowledge, no one is making them or selling castings.
If you are going to make an insurance claim, the price you paid for the whole engine is a good place to start.
Without the governor they are difficult to sell for more than 500-800. If insurance wants to pay only for the governor, go for $1,000. When the adjuster inspects the damage tell him you intend to keep the engine and damaged governor.
That said.... after you file a claim and get paid (the sender may need to file the claim) you might try to straighten it yourself as you may have nothing to lose at this point.
I Hope you find this usefull.
Gil