Two things to try before you cast it yourself. First, try to get replacement from Italeri. Second, see if there are any aftermarket props available. If these don't work, and you have to cast, here is my recommendation.
I am a big advocate of the J-shaped pouring sprue. You do NOT want to have resin entering top of mold, which will interfere with air leaving and seeking vent. Bend a J out of wire or something. Attach existing prop hub to top of the short leg of the J. Then glue a smaller vent tube from the top of the hub parallel to pour sprue up to same level as top of pour sprue. Suspend this contraption in a tube that will contain the mold and pour the mold material. Slit the mold, remove the pattern, replace the mold in the casing and pour resin.