First of all, the history of the ampersand (deriving from a ligature of a cursive et) is too short to be relevant to Classical Latin as @JoonasIlmavirta points out.
Wikipedia lists ZC (zetera et cetera) or ZE (zetera) as abbreviations of et cetera for classical Latin.
However, as @Marc points out, the American Society of Greek and Latin Epigraphy doesn't list it in their common Latin abbreviations. (Apparently, their list is based on inscriptions that were published in the French publication L'Année épigraphique between 1888 and 1993. The inscriptions are available on Wikimedia.)
I have been able to find a number of coins from the 16th century with ZC (et cetera) as an inscription, but of course that is not Classical Latin.