G’day

They look to be about 6” with a 1\2” axle size? Check the measurements to be certain.

The outdoorking online shop has generic steel wheels that look like they might do the job if they are the size they seem to be:

https://www.outdoorking-forum.com.au/tyres-tubes-and-wheels/lawnmower-wheels/universal-6-metal-wheel-wwp2378