Welcome to WikiTree, Dirk.
At
https://www.wikitree.com/genealogy/UNTERBRINK you will find the complete roster of WikiTree profiles for people with the birth name of Unterbrink. At the moment, there are only two other male Unterbrinks -- you may want to try to contact the profile manager to see if you can learn more about these men and find out if they've been tested.
You can also do your own detective work to find people named Unterbrink. Members here who have been involved with Y-DNA studies probably can give you some good advice on how to approach them regarding testing.
And your detective work should include beginning to add your relatives' profiles to WikiTree to build out your own known family tree -- and add to it with research.
And note that autosomal DNA tests can help to confirm relationships to relatives on any branch of your ancestry (not just the paternal Unterbrink line).
