I have heard that you need to have Qantas staff access to check actual loadings. Some travel agents may have access to this info too.
As a normal civilian, I would see whether you can see Classic Reward seats of the class that you want on the same flight (i.e. imagine you are booking a Classic Reward seat from scratch). If you see seats, that should give you a rough indication of availabilities.
If you have or know of others with subscription of Expertflyer, I believe that can also see the different fare buckets and what is available. However, that is getting a bit deep and not the actual loading (AFAIK). Hence, I would not get into it as I am not a subscriber and don’t know a great deal about this as well.