True, the importation of scopes and firearm accessories does not require a permit. However, exporting does.
The Australian Government monitors and controls the export of firearms and related goods. Firearms, firearm parts, accessories and ammunition, regardless of the state, age, completeness or working condition, are subject to export controls under Commonwealth legislation.
To export an item subject to these controls, the exporter must first obtain authorisation from a delegated officer of the Australian Government.
Export Firearms : Department of Defence
Scopes and accessories that are being exported without the firearm, are required to have a Defence Export Permit.
A Defence Export Permit may be used to export all forms of firearms and related goods including those where an Restricted Goods Permit may be used.
Permits are valid for twelve months from issue and are issued by the DECO.
There are certain circumstances for which only a Defence Export Permit can be used. These include:
-exports of five (5) or more firearms;
-unaccompanied exports; for example, goods being exported as cargo or by courier;
-exports of any amount of higher-risk or military firearms including their parts, accessories, and ammunition. This includes firearms referred to as Category C and D under State and Territory legislation, firearms over 0.50” (12.7mm) calibre and all automatic firearms;
-any firearm parts, accessories, sights, ammunition, magazines, etc, being exported without firearms; and
-firearms being exported for the purpose of repair, return, sales or as a gift.
To apply for a Defence Export Permit you will need to complete an Application to Export Controlled Goods and Technology form.
Firearms Permit : Department of Defence
While many people have done so without the required paperwork. I would suggest against doing so in the future.
Penalties
Failure to obtain permission to export is an offence under section 233BAB of the Customs Act 1901 and can attract a penalty of up to A$425,000 and or imprisonment for up to 10 years.
Export Firearms : Department of Defence