Stainless disks

I'm looking to re-bed some deck fittings and want some stainless disks to use as backing plates for the winches. I remember picking some up years ago from a place in Brookvale (?? wasn't Brookvale Stainless or Edcon) but can't remember where. Does anyone know of anywhere in the Sydney region that has stainless disks available off the shelf? something like 125 and 175mm would be ideal.

thanks!