Green’s Dictionary of Slang

something or someone excellent, first-rate.

1906		Sun. Times (Sydney) 16 Sept. 6/8: The beach is fairly packed every day, and the pier, rink, and casino are regular boskerinos.
1908		Sun. Times (Perth) 2 Feb. 1/2: Mr. Chriscroft (enthusiastically): O, he’s a boskerino is Stiff.
1911		Truth (Brisbane) 30 July 3/4: Bill Squires, ‘the bontoger boskorino,’ as the Newcastle miners and all the rest of Australia dubbed him when he was knocking down opponents like a bowler in a skittle alley, has arrived.