I've been getting an ever increasing number of attempted ssh login attempts to my personal server. These are primarily coming from various asian countries and Amsterdam. I've been firewalling out netblocks (only for ssh access) as this happens as I only need to allow ssh access from the US. Is anyone aware of a comprehensive list of netblocks assigned to various countries (or alternatively just to the US so I can whitelist it)? A google search turned up a few lists, but they are more specific than I'd like as they try to avoid smaller countries that share larger netblocks with known spammers/hackers/whatever. Most of these lists are targeted at blocking spam so they try to avoid the non-evil people. For this application I'd prefer to block everyone outside the continental US. Any suggestions?

Thanks,
-Mike