These are some tools I use to find domain information including DNS and possibly the domain registrar.
DNS lookup tools.
Security Trails: I use this to find previous https://securitytrails.com/
DNS Dumpster: For current Records and server locations etc: https://dnsdumpster.com/
These can be used to find domain reseller is in Australia
TPP wholesale: https://www.tppwholesale.com.au/provider/
Synergy Wholesale: https://synergywholesale.com/partner-lookup/ Synergy may also tell you if it is hosted with them.
Additional domain tools
Domain password recovery for au domains: https://pw.auda.org.au/ This will only work if the client’s email address is registered and not the reseller.
DNS Propagation: https://dnschecker.org/