Challenge: WHo can find this song for purchase?

So I'm trying to find an oldies song--"You're Mine" written by Robert Carr and Johnnie Mitchell, performed by Robert and Johnnie. Of course I-tunes doesn't have it and the only place I can think of is buying a whole Robert and Johnnie hits album somewhere just for the one song. mp3.com doesn't have it either. Does anyone know any elaborate online sites that sell older music?

I don't know anything about these performers or what their copyright situation is, but there's a chance that their music is not available for digital downloads. My go-to music site, ruckus.com, usually has the older, more offbeat tunes, but I found nothing for these two.

Appreciate the help, GrummanFan.