Yiannis Papadopoulos has done the right homework, OP, of finding Greek Wedding 1879 Melbourne, mentioning your ancestor.
For those confused by that: A Constance Ocass of Cerigo (= Cythera) got married in Melbourne in 1879. Tahlia O’Cass (the OP) is his descendant, and posted in that thread. The surname is clearly mangled from something Hellenic, and another descendent, Rita Kocass, posted that her family’s information was that the surname was Kokakarsas, and that he was from Skorpios near Ithaca.
1879 is extremely early, and both Ithaca and Cythera are completely plausible for migration from Greece that early (the only other place Constance might have come from was Kastellorizo).
Yiannis Papadopoulos is right that Kokakarsas does not sound Greek, and Google reports no such surname; given the penetration of the Web by now, including historical archives, I’m reasonably confident there wasn’t ever such a surname, and that something got mangled in the Kocass family tradition.
Given User-13249930999434776143’s answer that Kokakarsas is a bunch of Albanian vulgarities, it’s not impossible that an Albanian trolled the Kocass family about their surname, but I think it’s demographically unlikely. Neither Cythera nor Ithaca are Arvanitika territory, so I don’t think indigenous swearwords are the pathway for the surname either.
There’s a book on Cythera surnames (Καλλίγερος, Εμμανουήλ Π.: Κυθηραϊκά Επώνυμα. Εταιρεία Κυθηραϊκών Μελετών. First edition: 2002, Second edition: 2006), and Untitled Document lists the 258 surnames discussed in that book. None of them look like –(k)okas–. Kalie Zervos in that genealogy thread guessed that it might be “Cassimaty or Castrissios” , and Κασιμάτης and Καστρίσιος from the book’s list are indeed the only matches to Kas-. Karatzas isn’t much closer. Maybe Γεωργάς Georgás? But surely that would have just ended up as George.
There’s a monograph on Ithacan surnames from 1959 (Τοπωνυμικόν της νήσου Ιθάκης και επώνυμα Ιθακησίων / Σπύρου Ν. Μουσούρη (Φώτου Γιοφύλλη).), which is not online. There is a huge list of Cephallonian surnames (Ithaca being the island next door), compiled by Miliarakis in 1890: Anemi – Digital Library of Modern Greek Studies – Γεωγραφία πολιτική νέα και αρχαία του νομού Κεφαλληνίας υπό Αντωνίου Μηλιαράκη., digitised list at the end of Ιστορικές διαδρομές. From that list of some 1200 surnames, I get a few more possible matches, but they’re still distant: Oktoratos, Orkoulas, Kokkolatos, Kokkosis, Kaskanis, Kassandrinos.
The Melbourne Greek Orthodox Community has put up images of its minutes from 1897 to 1916: Greek Orthodox Community of Melbourne and Victoria. (Btw, that is *not* how you publish archival images. A simple PDF would have been a lot better.) Nothing jumped out as matching O’Cass there either, and Constance Ocass died in 1896. At any rate, he became Anglican, so his progeny wouldn’t have shown up in the Orthodox church’s logs—though as the genealogy thread says, one of his sons may have married in the Orthodox Church in Sydney.
I don’t think I’ve helped you, Tahlia. If you have more patience than me, you can pore over the 1897–1916 ledger, but I suspect your ancestors won’t show up there. If you *do* get somewhere, please let us know!