Owning a boat with the 1-3/8" shafts, I can tell you the 1-3/8" props you find on ebay are sort of nill and none. However, you can find props in the 1-1/4" range all day long.
If you sent in your existing 1-3/8" shafts and had them milled for 1-1/4" props, you would have the strong shaft and easy-to-find prop size. The plot thickens!