My local "manure/compost" supplies are 20L bags of chicken, cow or
mushroom compost at a nearby chicken breeder.

I know the chicken breeder bags his own shed scrappings as the compost,
but I expect he buys in the cow and mushroom compost (probably bagged)
from another supplier.

Does anyone know of such a supplier in SW Sydney, or wider afield?

Supply of cow and mushroom has become a problem and I' prepared to buy
in bulk (pallet, wool bale or 100 bags) to get it.