This is from VIC licensed dealer info sheet.
9.01 Classification of Deactivated Firearms
There is no provision under Victorian legislation to have a deactivated firearm removed from the Register of Firearms.
Deactivated firearms are required to be registered according to their original category of firearm and the owner must be appropriately licensed. The only event in which a firearm does not need to be attached to a licence is if it is deemed to be an exempt device under the Act.
9.02 Heirlooms Licence
For the purposes of obtaining a Heirlooms Licence, deactivated firearms should be certified as such by an Approved Firearms Identifier on the relevant form. Please email the Licensing & Regulation Division position based email account requesting an application form.
Looks like a dealer is your first stop in any case.
If it's still got to be licensed and registered, what are the chances it doesn't have to be stored like it did when active?