Hi, RajaSarma ... 

Are you still interested with address dropdown menu? You can looks my  system running  well in abantecart 1.2.0 and 1.2.1. Customer just select  country - zone - city - ditric -subdistric  when they  filling in the address field. Postcode/zip  automatically appear when subdistric selected.

The system running well too with shipping extensions distric base.



sorry  I am not influence  in English