Australia EOI, USA Police Clearence Certificate while in UK

Hi,

I need some info regarding the Police Clearance Certificate,
I am About to submit my EOI for Australia and came to know that I require PCC from all the countries that I have lived (for more than 12 months). I lived in USA for 1.5 years and I am not sure how to get PCC for US from UK, I have couple questions in this regard and I would really appreciate if you can help me or point me in the right direction.

1) Shall I wait till I get all my PCC's ( from India, UK and USA) and then submit my EOI.
2) What is the process to get PCC from US while in UK.

Thank you very much,
Ravi.