You do not need hundreds of numbers, just carefully read hundreds of ITU documents ;-).....

In fact blocking for instance 00xx7, 00xx8, 00xx9 and 00xx18 helps in many countries. "Suspiciouse" countries like bahamas should be blocked anyway because there is always somebody running a nice "money maker machine". And don't forget to block satellite gateways because the often are used ffom cruzer phones to make expensive calls (20 USD/min upwards)

However dial plans changing on daily base. Subscribe to the ITU page to get latest informations.