Reading through the rules for Concessional licence codes 404 & C4C shown below, there doesn't seem to be anything prevention you from making your own Historic Plates provided they comply with the rules.

Although it would be easier to just purchase these from the club at the wattle grove club rooms spare parts area or online through the Clubs Members Only area, in the Merchandise page

Concession Code 404 handbook states
3. IDENTIFYING 404 CONCESSION CODE VEHICLES

All vehicles with 404 Concession applied must display mandatory descriptive identifiers ie: ‘VETERAN’, ‘VINTAGE’, ‘POST VINTAGE’, ‘INVITATION’, or the now standardised word ‘HISTORIC’. (The other descriptive plates remain acceptable). An identifier label must be displayed on both the front and rear of a motor vehicle, motorcycles are only required to display one identifier label. ‘HISTORIC’ plates and stickers are available through the CMC and the Motor Museum of WA at Whiteman Park.These must be of minimum 25mm high lettering on a contrasting background. Motorcycle plate lettering must be no less than 15mm high on a contrasting background.

Concession Code C4C, Code of Conduct book states
4.3.2 Restricted Use identifier

The ‘Restricted Use’ identifier may be either a metal plate or a sticker. Labels on vehicles require lettering to be a minimum 25mm high on a sticker 18cms long and 4cms tall. Labels on motorcycles require lettering a minimum of 15mm high on a sticker 13cms long by 2.75cms high. The label must not interfere with the display of the number plate on the vehicle. This label can be downloaded from the DoT website and provided to a printing service to be produced as a sticker.

Hi Steven

it is an Either / Or, depending upon how or where you can fit them onto the vehicle as on some vehicles its not possible to attach plates. 

From the Code 404 Handbook
All vehicles in receipt of the Code 404 Concession are required to display an identifier label attached to or adjacent to, but not obscuring, each number plate displayed on the vehicle. For example, motorcycles, caravans and trailers are required to display one identifier label as they are issued with one number plate. Vehicles issued with two number plates are required to display two identifier labels, one front and one rear. Stickers are to be fitted to vehicle body above, below or immediately adjacent to the number plates when practicality prevents the fitment of identifier label plates.