Green’s Dictionary of Slang

1. a rabbit; rabbits as a group; thus rabbo! the street-cry of a seller of rabbits.

1904		Sydney Sportsman (Surry Hills, NSW) 21 Sept. 4/7: [P]enny plungers, wile rabbo vendors and bottle connoisseurs, lydies with reputations so loose that they flap in the breeze.
1916		C.J. Dennis ‘Rabbits’ in Moods of Ginger Mick 93: ’Eads down, ’eels up, ’e’ll ’awk us in a row / Around the ’arems, ’owlin’ ‘Rabbee-oh!’.
1947		Bradford (PA) Era 27 June 2/6: Australian slang favors words ending in ‘o.’ Thus ‘mucko’ for sailor, ‘rabbo’ for rabbit, ‘reffo’ for refuge and ‘susso’ for sustenance.

2. a street-seller of rabbits.

1908		Bulletin (Sydney) 1 Oct. 14/3: But ther rabbo on’y stood fingerin’ ’is whiskers ’n’ starin’ up th’ tunnel like a bloke who’ud missed th’ larst boat.
1915		H. Lawson ‘The Horseshoe and the Clock’ in Roderick (1972) 841: I gave Rabbo Mick a nod and told him to leave a rabbit at my place that morning.