Green’s Dictionary of Slang

oscar n.2

(N.Z./Scots drugs) an ounce (usu. of cannabis).

[Scot]G. Armstrong Young Team 126: ‘A half an Oscar n ten sweeties’.
[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 132/1: oscar n. 1 an ounce of marijuana.