If it’s a 1956 model, it would be 15hp. If it’s labeled as 18hp, then it would be 1957 or later. A few places for parts:
marineengine.com
vintageoutboard.com
timsoutboard.com
ganotech.com
Bob
1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20
“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."