Find on that field in the portal?
Search for info in the table where it sits is the best thing to do. So I'd search for "advisory" in the accounts table, gather the FK of the clients with ListOf, set a global to it and go to related records in the client table via a relationship that links the global in accounts with the PK in clients.
You can also filter the portal with a formula like this:
isempty (DROPDOWNFIELD); 1;
ACCOUNTTYPE = DROPDOWNFIELD
ACCOUNTTYPE is the field from your child table of course.
That formula needs to be entered in the "Sort Portal Records" definition.
The downside of filtering the portal is, that all records are being loaded, no matter which ones get displayed. Depending on your setup and the amount of records we are talking about here it might not matter at all.
Add a script trigger to the selection field to refresh the portal when it is modified and you should have instant results. To clear the search you might have to add a little button next to the dropdown to empty the filter field.