Presumably, the dealer is telling you the truth. All he can do is go by what his computer screen shows him.
My suggestion is this. Go to Case/New Holland's website and pull down their list of dealers. Start at the top and begin phoning them in sequence. Give the parts guy the part number. He can tell you if he has one in stock or not. If he does, then give him your credit card info and have him ship it to you.
If no dealer has one, then barring finding a good used one, have a machine shop make one.
Manufacturers are required to have parts available for six years after they stop making items that use those parts.