Pretty late to be answering this, but for what it's worth. I think this is what the Double Decker String Band sings on this song--which they say they got from the Dallas String Band---maybe Double Decker guessed at the second verse, but I think it's a good one, made up or not.

Someday you'll find the end of my rainbow
And maybe find a little pot of gold
Someday while running around
You'll find what we never found
A golden mist, a rainbow's kiss
They all fall down in a little pot of gold

Someday I'll be found to be missing
Angels carried off my soul
There is nothing I can do
While I am feeling blue
But chase those rainbows in my soul.