I have  a form like below image .

What I am trying to do is update this form data by using stainless form where user first Enter the "TV Station" Name form drop down and a script will run on User input on "TV station" to  populate all related "Network" name in the "Network" drop down field. After that User will go forward and select the "Network" name from populated value.

So on User input on "Network" Field I would like to populate the "Cable" name to corresponding field automatically. 

For Instance , If User Select the TV1  from "TV station" and then Select Me-TV in the Network Field. Then a script will run to retrieve all related "Cable" name to fill corresponding Fields. 

I can populate Network name in the "Network" drop down ... but I can't figure out the script (on User input on Network Field) so it will retrieve all related cables name based on two selection ( TV station and Network)

Below is what I am looking for..

could any one please help me that would be really appreciated.

Note: TV station and Network fields are the Look up field of "TV station"  form and "Network" form respectively.

Regards ,

Arfater.