I just had another idea. If you look up dastelefonbuch.de (they have an English page if you do not know enough German) you will find there are just 75 entries for Hruska. If any of these seem to be in the area you are talking about it might be worth writing and asking if they know anything about name changes. If there is no one in the area you want it might still be worth picking out a few and writing a polite letter. It would only cost a stamp or two and could provide a lead, if it doesn't you have not lost much. Good luck