[Off Topic]: IP Listings based on Country?

I have talked with engineers in the past that like to block all IP addresses from countries such as China for example in an effort to quall spam and other malicious activities. Where can these listings be found? I would like to block entire networks at our border router for countries we don't do any business with or have a need for them contacting us. We have been seeing an increase of malicious activity lately and about 90% of it comes directly from China and the other 10% likely originates there as well. Most of it has been low-level script-kiddy stuff, probing for open relays, trying default user accounts, and other amateur stuff but can't be to cautious. thx, rhugga