well heres a suggestion of getting the country of the ISP..
maybe use explode to get rid of the last . cos thats the bit where it specifies the country
In Evilwarius theres one that does kinda what im saying and it also has the country prefexes like au is australia etc.
From that you can use the ISP to get more IP addresses that come from the ISP and block those or just block the whole ISP by doing what i said.