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.
There are a couple of website online too that you can hire them from and they will post it out to you.
If you google "Labour Tens Hire" you will come up with some places (I dont want to copy in the links in case I get in trouble)
I'm looking to Hire one aswell (I'm in Brissy) my hossy has them but I could only use it once I get there and i want to be able to use it at home when I first go into labour.
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