57hoon,
Here in Canada and the USA we have many sources for replacements for the soft top. I'm not familiar with what you will find available in Australia, but a Google search for 55-57 Thunderbird convertible tops should yield hits from many different suppliers in North America. These suppliers have kits made specifically for these small birds. They run from just under $200 USD to just over $450, depending on whether you want vinyl or Stayfast Cloth. One such supplier is National Parts Depot. Their online catalogue is
NPDLink | National Parts Depot
Any of the suppliers could give you the shipping costs by email, if you can't find an Aussie source.
Regardless, it is not a job for the first time DIYer. It might be after having assisted a professional with installing two or three first. Good Luck!