I have no idea but I know that all those types of signs are ussually rented by the REA from companies that do the graphics and erect the signs. All the signs I have looked at (just sold and bought) have a sticker of that company on the back so I would find one in your local area and look for the company and just give them a call.
There is a company in Sydney that manufactures a lot of those Real Estate signs they are called Charisma Signs 02 9678 9540 speak to Martin Borg tell him James sent you he will look after you.