I suggest you send a mail to Dr Alois Ruhri, head archivist the Catholic church's diocese office in Graz at:
archiv@graz-seckau.at
giving them as many details as you can regarding names, dates and places. However the generally do charge 25 Euro for their services.

Another place for the same enquiry is:

austria-l@genealogy.net

where hobby genealogists are more than willing to help and usually come up trumps.
Happy hunting!
BeatrixAnna