Try the following:
1) go to http://www.dejanews.com and do a POWER SEARCH for [ sea songs & shanties ] .. set AGE to OLD/50 or more
2) go to http://www.dogpile.com and search for same thing as above.
3) go to dogpile/search: [ sea songs & shanties | american shipping ]
may take you a month or two to read all of it