While dabbling in electronics for a hobby is a very enjoyable pastime, if you are not licensed to work with 240V AC, then I would leave the actual work to someone who is licensed.
About the actual PID controllers and SSRs themselves.... they can be easily obtained in Oz from a number of suppliers who cater to Industrial Process Control. In the end you get what you pay for, as with everything..... the more features and control options you require, the more expensive will be the controller. It would be a good idea to identify a budget limit before you embark, otherwise you may be surprised by just how expensive this can become.
You also need to be aware that this mod, like most of them, will probably void any remaining warranty on your Silvia so that needs to be considered. If and when you do go ahead with the mod, you should try and identify a method that wont leave its mark behind in the event that you may want to sell Silvia sometime in the future.... unwanted extra holes in Silvias metalwork would definitely reduce her resale value.
Anyway, just so that you have somewhere to start sourcing information, here are a couple of Industrial Control suppliers to whom you can start directing inquiries. They are both reputable firms and have their own preferred vendor products to promote, as do they all, but you will get good advice from them once you explain what it is that you intend to do. One is....http://www.onetemp.com.au/ and another is....http://www.eurotherm.com.au/index.html. Plus, if you do a Google search for Australian based Industrial Control suppliers, Im sure you will identify several others.
Hope this enough for you to be going on with.... all the best,