Aussie beans tend towards the soft and mellow end of the scale. Andy has some amazing Mountain Top Estate in BeanBay and you may also want to consider 'Basalt Blue' from Coffees With Altitude from Far North QLD and Green Cauldron from the Byron Bay hinterland in NSW.
By the way... there is no real need to aim for lighter roasts to avoid those nasty burnt flavours... especially for espresso. Medium and medium/dark roasts can also be smooth and mellow yet also possess the sort of rich, full body one tends to look for in an espresso. Just make sure you pay attention following the start of First Crack and don't let the roast get away from you. Slow things down and and aim for dropping your roast at the first hint of Second Crack and cool the beans as quickly as possible and things should be sweet as.