The full answer
The NDIS Commission publishes a list of around 30 Approved Quality Auditors (audit bodies) on their website. Some specialise by region; some by service type. Most service all states. Selection criteria: pricing (get quotes from at least three), turnaround time (current capacity matters), specialisation (some are stronger in SIL, others in allied health), responsiveness during the audit window. Provider Scale's $999 service includes a recommendation based on your scope.