state archiv - civilregister
http://www.szukajwarchiwach.pl/search?q=Gwda+Wielka&wyni...adress of the state archive
http://www.koszalin.ap.gov.pl/index.php/de/kontakt/koszalin....i do not know, which agencies you contacted. if you ask the archive, you can do it in english via email. the email should include your postal-adress. the answer will be in polish. what they found, with the cost for search and copy.