That's an issue we seem to have to live with. Perhaps as the Gnutella netwk improves & LW makes the most of it, we'll hopefully see it happening less. (Add to that the increasing popularity of Gnutella & thus larger no's of sources.)
Why not ask your partner to burn/copy to zip or something for you. Then if you add that to your shared folders, you've increased the sources available 4 others. Somebody else on the forum might have an answer. It's annoying having a file almost complete & difficult to find sources! All I can really suggest is that you continually search & use as many variations of search criteria as you can. Personally I only have a dial-up, so I have same issues.