I suspect that his name is an anglicised version of the perhaps Croatian or Serbian original. I've tried the Croatian and Serbian translations of 'brown' and they don't find any hits, so his original name is likely to have been something that was easily rendered to 'Brown'.
Try searching that region in FamilySearch using wildcards on both forname and surname (ie. Luca* Br*).
That finds Lucas, but also Luca, Lucam, Lucae - Lucas would be the logical choice for him in NZ from those. Br* finds Bradich (and variations) and Brosn, etc.
I think your best chance of identifying him is to try and interpret his wife's maiden name. Can you send an image? Alternatively can you interpret any letters, you should try searching with wild cards using the letters you can rean and replacing single unknown letters with ? and multiple unknown letters with * - that might come-up with a limited number of possibilities, which might help with the interpretation.
