Here is some more information on Karścino (Kerstin) itself: http://en.wikipedia.org/wiki/Kar%C5%9Bcino
In Karścino there is St Mary of Czestochowa church which belongs to St. Peter and Pablo parish in Robuń . It means that all the records concerning people coming from Karścino (so births , marriages, deaths, etc.) suppose to be collected in this particular parish.
More information about the parish ( it is in polish but I think you can google-translate it, if not- then just let me know if you'd need any information from there): http://www.koszalin.opoka.org.pl/new/p.php?m=6&p=75
Also there the copies of these records are in Kalisz Archdiocesan archive.
As far as I've learnt until now the following are available regarding Karścino:
– births: 1868-1927.
Probably all the rest is in the parish chancellery.
Please let me know if I can help you with anything else,
Any questions, just write me on:firstname.lastname@example.org
Good luck in your research anyway,