I don't know if you have found this or not, but it is a fantastic resource.
http://matriky.archives.cz/matriky_lite/
The link will take you to digitized baptism, marriage and death records from the Czech Republic. There are quite a few records digitized for Mahrisch Schonberg (Sumperk). It takes a little playing with to figure out how the records work and patience to figure out the handwriting (Cyndi's list has links to deciphering the German script used at the time)but the information found is invaluable.
You have to use the modern name of the place for a search.