I'm totally with you on this one. My favorite tune ever - if we're talking about the same one. There are several. At least two reels and a slow air (my favorite). Even the slow air, I've heard it played in G with the middle C's sharp or natural (my favorite). John Trillian has many of them in his index. Here's one (a reel) with chords...

href="http://trillian.mit.edu/~jc/cgi/abc/gettune?F=PDF&U=/~jc/music/abc/Contra/RJ/Set32.abc&X=17&T=GREENFIELDSOFAMERICA&N=GreenFields">http://trillian.mit.edu/~jc/cgi/abc/gettune?F=PDF&U=/~jc/music/abc/Contra/RJ/Set32.abc&X=17&T=GREENFIELDSOFAMERICA&N=GreenFields