Have you considered writing (in German) to the firm and asking if they happen to have records of you rifle? This would be the simplest way.
You're very lucky that this maker is still in operation as many aren't!

Ludwig Borovnik KG
Bahnhofstrasse 7
A9107 Ferlach, Austria
Tel (04227) 2442, 2249, Fax 4349

http://www.ludwigborovnik.com/geschichte.php