Does anyone know where I can buy an instrumental version of "You Sexy Thing"? The local theatre guys approached me for a production of theirs but I can't seem to source it anywhere.

have you looked into karaoke versions of 'You Sexy Thing'?
Sunfly will more than likely have it on one of their collections, Zoom may have it as a download (MP3+G)

Thanks for the suggestion. I did come across this version (http://www.karaoke-version.com/mp3-backingtrack/hot-chocolate/you-sexy-thing.html), but it didn't sound anywhere near as distinctive as the original. Would Sunfly/Zoom versions be the same?

You could always use Karaoke song making software to remove the vocals from the original I guess.

Have you any found any that works? I tried one bit of software with a "vocal reducer" that strips away most of the backing track as well and leaves you with a warped mess.

Yes I had a dabble with Power video Karaoke a few weeks back. I was only testing it really but it took the vocals from a K.C & The sunshine band track away no problem.