You can hire them from places like Hire For Baby, they have branches all around Vic. There may be other baby stores that hire too, I know ABC Bitz For Kidz in Kew hire them out.

I highly recommend Amby baby hammocks, they are really well made. To buy new they are about $360 (you can buy them directly from Amby) or you can pick them up second hand. Try some second hand baby stores, I get them in occasionally (PM me if you want more info ). Otherwise you could try eBay.

HTH