Some very coarse SiC stones can work as flatteners. The problem is they tend to clog and need a lot of cleaning with a brass brush or something similar. Others, just clog way too fast to be practical. I don't know enough about yours to say which it is. If I'm not mistaken, the "Peacock" Duckfat recommends is an SiC of "the good type."
A ceramic flattener, something like the Norton or Naniwa (around $25) with grooves cut in it is easier to clean, and are also decent, budget flatteners. Unfortunately both types, SIC and the soft, coarse ceramic flatteners wear quickly.
Wear doesn't just mean they get used up, unfortunately it also means dishing. So, in addition to cleaning, the flattener will also needs regular flattening or cannot be used as a "reference." Still, even with their problems, inexpensive "flattening stones" are a good solution for beginners or those who don't do much sharpening.
Another alternative is a coarse diamond stone like a DMT XC or XXC (don't know what you've got in Oz). They're very efficient, easily cleaned, and so on. The limitations are size and price.
Ice Bear is King's best, clay-binder line. I've never owned an Ice Bear, but as a clay binder stone and should be very easy to flatten on a flat piece of driveway, or 80#, then 220# wet-dry sandpaper. When the sandpaper clogs (which will happen even with a lot of rinsing) or wears down, just throw it away. Sandpaper is cheap, large sizes make even flattening and "referencing" your progress simple; but it's slow, messy, and clogs quickly.
Dry wall screen, if you can get it, is longer lasting and easier to clean than sand paper -- shoot for 180#. It's still a lot slower than a diamond stone like a DMT XC or XXC, but that shouldn't be much of an issue with your soft stones. A secondary benefit is that you can buy large enough pieces to flatten the stone perfectly and all at once -- which makes referencing easy. Here in the US of A, $11 buys a two or three years' supply of 9" x 11" screen (don't know what it would set you back down undah). Of course, you'd need a piece of glass, metal, stone or tile to lay it on, too. So figure another few AUD.
Most clay binder stones, like your Ice Bears, dish quickly -- especially combi stones where each grit only has one side. You should probably flatten your 800# at least every other time you use it.