I will go to the state or church archive in Poland and look for a birth record of your ancestor. If the parish is known and the records are available I’ll find a record and make a copy if possible or order it. After obtaining it I’ll upload the scan. I’ll also provide translation of a document. If parish is not known or the religion is other then roman-catholic I’ll attempt to use other sources of information first to determine it (like databases of holdings of polish state and church archives).
Krakow archive contains some metrical documents for nearby parishes outside a town as well.