How to reference states not in the USA State enum list?

Hi is there a way to reference states belonging to countries like UK or AUSTRALIA?

I am adding a Customer Address book and want to add a state from UK and AUSTRALIA
.NET Code snippet below
CustomerAddressbook[] addressbook = new CustomerAddressbook[ 1 ];
   CustomerAddressbook addressbookElement = new CustomerAddressbook();
   addressbookElement.addr1 = customer.addLine1;
   addressbookElement.addr2 = customer.addLine2 + " " + customer.addState;
   addressbookElement.city = customer.addCity;
   //addressbookElement.state = State._xx
   addressbookElement.zip = customer.addzipCode;
   addressbookElement.phone = customer.addPhone;
   if( customer.addCountry.Trim().ToUpper() == "AUSTRALIA" )
   {
    addressbookElement.country = Country._australia;
    addressbookElement.countrySpecified = true;
   }
   else if( customer.addCountry.Trim().ToUpper() == "UNITED KINGDOM" )
   {
    addressbookElement.country = Country._unitedKingdom;
    addressbookElement.countrySpecified = true;
   }
   addressbookElement.defaultBilling = true;