Indirect Data Validation

Hi Excel Experts,

I need some help on data validation. I have in tab Checklist which the data is coming from Sheet3 Column A but I cannot use data validation as it has a lot of duplicate records.
Bigger problem is for example if I select "DBMW" in tab Checklist Column C4 I only want to see the countries in Column D4 which are listed in tab Sheet3 which column Service Tower = "DBMW" and so on for tab Checklist column E4 I want to only see the locations available if Sheet3 Column Service Tower="DBMW" & Sheet3 Column LBU="CA".

I tried to use the Indirect formula but I am not getting the correct result. Anyone there able to help me with this? Attached is the Excel File sample and how I want it to look like.

Kind Regards,
Mark.