Retrieve child key based on parent key

Hi,

I have created a user defined table named as "District" in Order Management Module. The purpose is to enable user to create new entry of District ID as based on parent key which is retrieve from Sales Territory ID. Now, I would like to retrieve these configured child key (District) in Order Entry screen. However, i would not be able to find the related adapter for child key. All i would find is adapter which would give me access to configured parent key. If anyone would provide any opinion on solving this (ex:any related functions to retrieve child key directly in script editor? )