Limewire still shows the source of the file... it may be turned off in your system.

Since you did not indicate what platform you are on I will assume it is windows... right click on the 'header' of the search window and a drop down list will appear... be sure the 'location' check box is checked... this is the source IP.

Go to tools / Options / filters / hosts and add the offending IP to the list marked 'filter hosts'. Done.