Chachi:
Went to the FAA Certification Data and downloaded the A6CE file which covers the Skymaster. On a 337G the number you give (D2AF34C306/78CAA-O) is the right one through aircraft s/n 1748, but later units use D2AF34C310/90DEA-12. No 337G uses D2AF34C59-NP. My suggestion is that you call everybody that overhauls propellers to see if you can find one. Also try the yards which part-out Skymasters, with emphasis on Don Nieser at Commodore (for phone numbers and a longer list of yards go to
www.SkymasterUS.com and click on "Purchasing Parts").
Good luck.
Ernie