Always worth asking again if you don't get an answer first time. The -ic ending is the "son" ending, as I'm sure you know. Not added to given names only (e.g., Markovic), but also to occupations (e.g., Kovacic) and nicknames (e.g., Babic). An online Croat dictionary doesn't recognise Brc as a word, with or without a diacritical mark over the c. I'm wondering about an old forename , Boric, which I've come across; described as a diminutive of Borislav. Is it likely that it could have become Brc in the process of forming a surname?