Grodno State Archive accept inquiries from everyone via email http://archives.gov.by/index.php?id=377130
Their services cost money http://archives.gov.by/download/preskurant_grodno_2016.rar

You can request general church records and elections and conscriptions into Polish army between 1921-1939. The request has to be made in a prescribed format in Belarusian or Russian languages, or it will not be considered.