Calvin, I assume this is the song you're referring to. It was made famous by Glen Campbell, but Carl Jackson wrote it.
The bad news? The song is under copyright, so you won't find free tab anywhere.
The good news? The song is definitely do-able on a dulcimer with a diatonic fretboard.
The version I link to above is played in the key of E. My advice would be to tune your dulcimer to EBe. You will still be in a 1-5-8 tuning, so all the chords and fingerings you know for DAd will still work. Then you can play along with the song. Once you have the basics of the song down, you can tune back to DAd and play it just the way you had been.
You can probably find chords and lyrics by searching the internet. I just did a quick listen and the chords in the key of D are D, G, Bm, and A. The structure of the song is simple, with a verse and a chorus. The melody seems to have no accidentals, so you'll be able to get it on the dulcimer.
If we could meet down at the pub, I'm sure we could figure it out together.
Dusty T., Northern California
As a musician, you have to keep one foot back in the past and one foot forward into the future.
-- Dizzy Gillespie