Here's a thread that has various posts on extra DNSBL definitions, including ones for blocking countries other than those in the default list:
http://www.spampalforums.org/phpBB2/...p?t=3129#16949
I have Spampal set up to be quite strict:
Blacklists... Public blacklists... Click "Pre-created filtering strategies" Choose "Aggressive"
Blacklists... Countries... Check all except America