Extracting row labels from pivot label to create conditional dropdown menus

Ok so I have a pivot table and it has rows and subrows. The Pivot table in excel automatically knows which subrows are present for each row. In the example attached, the pivot table knows that for the 18-20 Age Group, the only two parties which are present are Declined and Democrat.

I would like to create a conditional dropdown list. If the user selected 18-20 Age Group in a dropdown list, he will get only Declined and Democrat in the dropdown list for Party. I could do this manually but there is a chance that these rows and subrows change when the datasource changes so I want Excel to do this automatically.

No Macros please.

Please help. Thanks!

Thanks Andy! I can't find where you used the INDEX to build the range for PARTY_1820.
Thanks for the help!