For a start, many of the spammers use dynamic ip addresses which change multiple times in a week, perhaps even multiple times in a day due to their own tools of achieving this.

There 'are' ip blocking lists. A few can be found here: phex - Revision 4345: /phex/trunk/src/main/resources/phex/resources/hostiles

Another custom made one can be found here: Hostiles List.

The new LW 5.0 will have built-in hostile list once it is released. Phex already uses one which is an adaption between those in the first link.