Has anyone checked with the district civil registry (РАЦС = RATS in Ukrainian; ЗАГС = ZAGS in Russian)?  Ostroh is the administrative center of its district, so the civil registry for the whole district would be there.   Looks like their phone is +380 (3654) 2-30-92.  Email: vcs@... 

Phone calls should probably be done by someone fluent in Russian or Ukrainian, but emailing in English might actually work.  Chances are reasonably good that someone in the registry knows English, or they can recruit someone to translate.

-David Mason, Los Angeles