Kristy70 has beaten me to the first part of my answer. EveryHit.com lets you search the UK charts by date.
Once you've done that you just need to know where to find the downloads. The obvious answer is Amazon MP3. (If you look at the post immediately before yours in AB's 'Music' section, you'll see that we managed to help someone find an obscure Bernard Cribbins' album track, on Amazon MP3, for 69p. There's not much they haven't got!):
http://www.amazon.co....e=UTF8&node=163937031
Chris