Spares in Oz are hard to come by. I normally buy my spares from RC-Model (
http://shopping.rcmodel.hk/). Others also use RC Market (
http://rcmarket.com.hk/) and RC Champ. Generally the only spares needed are arms, castor blocks and rear hubs - all of these can break when you hit a board. Just stock up on a few of these bits when you buy the car and you'll be sweet. I have been running the car for almost a year and I'm still on original belts and pulleys. I haven't even had to rebuild the diff although I built them up with ceramics balls and adhesive backed diff covers. The 416 is an awesome car and with all the help on this thread, you will also have a great knowledge base to back you up.
The HPI springs have been used by the team drivers with some success. A few of us here have also tried them and they feel a little nicer - some say more progressive than the Tamiya springs. I have been running the HPI Blues all round lately and the car feels glued with them.