There are plenty of places in Melbourne who hire chains try one of those.

I had the same problem with my Land Rover a couple of years ago. One size oversize tyres and no chains of the correct size at the hire place in Bright or somewhere that way. As the sun was shining and the forecast was great I just hired the standard size chains knowing that they would not fit, that nobody ever checks that you have the correct sized chains and that I (hopefully) wouldn't need them. I didn't need them so it worked out well. I wouldn't do that with a 2WD car and I certainly aren't recommending that anybody else does it.