No I don't know of a Script but I can tell you how to do this with Quicksilver. You select the song in iTunes press command-esc which sends the file to Quicksilver, and then you type compose email (with the mail plug-in installed). And then type in the recipient of the mail and hit return.
It will open a new mail for you addressed to that person with that song as an attachment. This is just one of many ways of how Quicksilver has changed my Mac experience.
The way I described it is a simple run-down. At first it might not be as simple as this, but once you get the hang of it (which takes 10 minutes or so) you'll be convinced it is easy.