its rather simple...

a fact: there are no servers supplying files...none at all, cept the ones YOU and I run as users of the gnutella network...

so, since it's individuals supplying the files, said ppl come and go...and if you aren't sharing any files, it just may be that said suppliers are disconnecting you, and possibly blocking you with their firewalls for being a leecher on the network...who knows?

so, the only solution is to just keep trying...

one trick would be to log their IP address, and try direct connecting to them..this will allow you to 'find' them if they are on another 'node' of the network