I don't know where you're from but I'm from the Netherlands and own a FJS400 from '08.
In Europe there are lots of spare parts to be found on the interweb
The only difference between the 600cc and 400cc is in the engine parts. Almost everything else is interchangeable. My first SiWi was a FJS600 from '01 and I have discovered that they are 90% identical.
I wish you many safe miles and lots of fun.
Greetings from the Netherlands