Try Vtrader. They are expanding in San Francisco, and have both equities and futures guys there. I am looking into trading there myself if I decide to go back and do the office thing. Trading solo means reading ET far too much!
You forget that Australia is part of the commonwealth and many Aussies have ancestral roots via parents or grand parents which is why they can return and get passports. Also UK immigration is a joke. But the USA has the hardest immigration law in the world next to Canada so your chances are virtually nil. But you can check this out on the web on dozens of websites, books too have been written and so for you to ask here is just lazy or maybe you just want people to build up your false hopes. My advice is if you really want to get there then you need to take it more serious for a start. I have known many people who have moved to the Us and most struggle to adapt to the differences, besides you will only get sponsorship as an employee and even then there are many stipulations such as minimum income and and degree requirements alongside a yearly quota of visas issued. even then you are only considered temporary and may never get a green card and have to leave after 6 years. But do your own research and you'll discover this. Otherwise it will always be just pie in the sky daydreaming.
Its too bad you want be able to trade in California, its like paradise over here in terms of weather, social life, girls, and overall quality of life. One of my favorite things about California is that you are right next to everything. I live in Northern California and I am 20 minutes away from beautiful San Francisco, 1 hour away from the Santa Cruz boardwalk/ Surfing, 40 minutes away from Napa valley wineries, 3 hours away from great skiing/gambling in Lake Tahoe, 6 hours away from Los Angelas, etc. The weather over here is amazing I use to live in an area where the temp never went below 60 or above 80. You should try your hardest to come here, even if you have to do it illegally. Who knows, you might get granted amnesty along with the other 12 million illegals out here.