When I can't find anything, the first thing I do is go to the guitar tab sites and get the chords. If nothing else, it gives you the roots to get started with.
Listening to the video (and the song on iTunes), he uses a lot of passing notes between roots and does some running at the end of the second line of the chorus, but other than that, it sounds fairly straightforward.
Here's what I use when playing the song on guitar:
Intro:
[C][Em][C][Em][D]
Verses:
[Em] [G]
See...
[D] [C]
See...
[Em] [D] [Em]
Down by the water.....
Chorus:
[Em] [D] [Em]
The season.....
[Em] [D] [C] (fill in here)
The summer....
[Em] [G]
So knock me....
[D] [C]
But I....
[Em] [D] [Em]
Down by the water........
Harmonica Bit:
[C][Em][C][Em][D]
Instrumental Break:
[C][Em][C][Em][D]
[Em][G][D][C][Em][D][Em]
Outro:
[Em] [D] [Em]
Down by the water....
You can put the pieces of the puzzle together, yourself, but this song is similar to most folk tunes in that they follow the same patterns throughout.
Good Luck,
'Bolt