It sure is annoying when u get a song stuck in your head Ty. Its funny, as I had the same thing happen to me just a few weeks ago. Seems to afflict me with the most monotonous regularity LOL.
Anyway, indeed do have a look around sites like You Tube etc.. You just might get lucky and find the version of the song you are looking for Ty.
However, I doubt you will find it, as in my view the piece of music you're referring to, is most probably one of Joseph Conlans instrumental underscores that was likely added in place of the original music. And as far as Im aware, the tour of duty underscores that Mr Conlan wrote, are unfortunately, not available publically.
Either online, or on CD.
Craig the Hum90 webmaster, actually interviewed Joseph about the music that was written for Tour of Duty, because he was getting so many fan questions re the music
(you can read the interview transcript here
http://www.hum90.com/joseph_conlan.htm
Cheers Ty.

--Previous Message--
: Lindy, I think you're right on the song, I'm
: listening to the covers of it on Youtube.
: Now I just have to find out the one who sang
: the version that's playing in my head.
:
: Thank you for the help!
: