"Mary walks amid the thorn" can be easily arranged for SA. Here is a very straightforward example from CPDL; I would choose a different ending, though, because to my ears a sixth is not "ending able", but YMMV. A metric English translation (if it is not already in your hymn book) can be found on Wikipedia.

There is also a sacred contrafactum to "Une jeune fillette" (AKA "La Monica"): "Ye sons of men, in earnest prepare your hearts". The original song was the greatest hit in the 16/17th century, and it is still appealing today. The contrafactum is unrelated to the sad original text, of course, but refers to Advent as a time of preparation for the coming Saviour. You can easily add a second voice to the melody and the second part even invites some imitation in the fourth.