I am just looking at an old songbook I picked up at a flea market for a quarter called, "357 Songs We Love to Sing" each is written in from two to four parts- there is a four part arrangement for "Loch Lomand", and a three part arrangement of "The Minstrel Boy" half a dozen each from Thomas Moore and Robert Burns--printed in 1938--

There are many collections like it floating around, as singing was once very popular(before families had two working parents and a TV in every room) and every school of every size had it's choir, choruses and glee clubs, as well as any number of informal singing groups--

You may find a stack of these in the back room at church or in a corner of the school's music library--and a large, old library in any downtown will, more likely than not, have a few dusty shelves of these items--The tastes of past times are not are own, so much of what you find will not satisfy contemporary definitions of traditional music, but there will be some gems that you can recover with the aid of a good photocopier or, if need, a fair music copiest-