Вот так получилось!
var str = '...ITowns.initialize({"groups":null,"towns":[{"island_id":154563,"plenty":"stone","rare":"wood","population_extra":0,"has_conqueror":false,"researches":{"berth":true,"conscription":true,"mathematics":true},"favor":500},{"island_id":156890,"plenty":"stone","rare":"iron","population_extra":0,"has_conqueror":false,"researches":{"berth":false,"conscription":false,"mathematics":false},"favor":500}],"tmpl":...';
alert(str.split("\"towns\":")[1].split(",\"tmpl")[0]) ;
Не знаю насколько правильно... Но буду использовать.
PS. как запустить скрипт на форуме?