Turns out I don't have that particular tune, but a quick Google search for "Lemmings 2 Amiga music" quickly leads to
this site where you can download all the Lemmings 2 music, which was probably where I got them in the first place. The downloads are gzipped so you'll need to find a suitable program to decompress (WinRar, 7zip, etc.).
The intro tune is called "maintune" on the site.