Physio dept at the Mater have them - it's $20 for hire, $20 for the pads and $50 deposit. Includes a class on how to use effectively, and you get to read other ladies' experiences with them. They like to book you in for that fairly close to your due date - mine was 3 weeks before.

Hire for Baby also have them.

Make sure you get the labour TENS, not just the regular one, so you've got that boost button.