Alex

You might also look at the songs Malcolm Laws indexed. He published two books, Native American Balladry and American Balladry from British Broadside. They are out of print, but the books index, but do not include, the songs. Examples of all of the songs he indexed are in the Digital Tradition (it took me a couple of years to find and enter them all). If you search for Laws, you will get a very long list of songs. Again, not all will be what you want, but a lot of them will be. What Laws did was to set up a series of categories and give each of them a letter designation and then a serial number within the category. Since I own only one of the two books, I can easily give you examples of the categories in the second book:
   J War Ballads 23 songs
   K Ballads of Sailors and the Sea 43 songs
   L Ballads of Crine and Criminals 22 songs
   M Ballads of Family Opposition to Lovers 39 songs
   N Ballads of Lovers Disguises and Tricks 43 songs
   O Ballads of Faithful Lovers 41 songs
   P Ballads of Unfaithful Lovers 40 songs
   Q Humorous and Miscellaneous Ballads 39 songs

Hmm, that looks like more of the songs you want are in the first half. I don't have the formal designation of the categories, but I can guess from the lists of songs
   A War/Battles 26 songs
   B Cowboys 27 songs
   C Lumbering 28 songs
   D Shipwrecks 28 songs
   E Outlaws 26 songs
   F Murders 37 songs
   G Disasters 33 songs
   H (Not sure what they have in common) 31 songs
   I Negro Songs 20 songs
   
Of course there was the problem of what is a song fit more than one category.

Also check out the thread Basic Folk Library