What kind of hosting does this site use? If you have a dedicated server or a VM, ConfigServer Firewall (http://configserver.com/cp/csf.html) is a great free way to filter IP addresses. The install is really simple (its just an iptables wrapper), and the GUI is fantastic. It has login failure detection (brute force detection) and supports importing IP addresses from public ban lists and keeps your own local ban list. I believe you can also ban countries, but that would be difficult here as this is a multinational site. I use it on my cPanel webserver which was receiving about 1 - 5 attacks per second. For public ban lists, I like Spamhaus's Composite Blocking List, and their Zen ban list (http://www.spamhaus.org/zen/). There is also Project Honeypot's BlackList (http:BL). If this site is on a shared hosting plan, you may be able to find a module for either the forum software or the content management system that will let you import these ban lists.
Also, if you want to check the validity of an IP address, go to www.senderbase.org and type it in. It will show you if the IP sends a lot of spam, and if it is on any block lists. It will also show you if there are any other bad IPs in the block. For example, that 182.186.x.x block has 17 blacklisted IPs in it: http://www.senderbase.org/lookup/?search_string=188.8.131.52 The Project Honeypot website works the same way.