I have two great sources. The first is Engine Blade and Prop in Milwaukee, WI. Don Griner who is a retired Evinrude guy has parts for everything from about 1923 and forward. Don does have an Internet Site. Try searching on Engine Blade and Prop.
My second suggestion is AOMCI which stands for Antique Outboard Motor Club, Inc. Search on AOMCI. On it are several links on the AOMCI site to various folks that have parts.
I have about thirty antique and classic outboards, and will let you know that once you try to restore it can be a bit expensive, although the old Evinrudes and Johnson’s cost much less then the Mercury motors.
If you need paint or decals let me know, and I can supply a few contacts. if you need more info about the motor just forward the serial number.
Finally, jsut being curious, but what is the condition of the motor.