Well, Jeff, "How Can I Keep From Singing" is real easy. It's in lots of hymnals and songbooks, and it's in a McCutcheon songbook you can order by clicking on his Web site, http://www.folkmusic.com/. I'll guess that if you order a songbook and ask nicely for the "Down Came an Angel" song, they might be able to find a copy for you. Even if you don't order a songbook, they might.
-Joe offer-