I know how frustrating that can be! Having been a dial-up user not long ago, it would've been even more difficult for me. lol Search results can go stale after a period of time. I'd suggest you re-search for the source(s). I don't know what limitations you have set at present, but you could also temporarily lift any you have on Speed & Quality (LW's menu Tools-Options-Searching or for mac that's Options-Searching & OSX that's Prefs-Searching.) Doing this 'might' help you to find more sources for that rare file. If your version of LW has Local Preferencing in Advanced, you might also untick this. But this is generally related to obtaining files from other cultures, etc.

One other idea I have is an attempt to connect directly with them. If you can get their IP address, you can try adding this in LW's Connections window. However the LW Beta 4.1.7 might be moe successful at that b/c it has a direct connect search option.