The Chiang Mai Consulate “is not authorised to provide notarial (document) services” (such as statutory declarations, witness signatures, residence certificates or certified true copies), in accordance with the Consular Fees Act & DFAT policy.
It can offer referral information.
Notarial services are only available at the Embassy in Bangkok, with an appointment. Note – There are limited notarial services available by mail with Embassy in Bangkok.
Link for more information – see this Embassy webpage
Australian Consulate Chiang Mai 