How to get clearance certification from US

Hi All,
I am from India, and I am looking for some inputs with respect to 489 application to south australia.

i submitted all the relevant documents in immi site and got a query to submit Police Clearance Certificate again to my application.

i submitted clearance certification from India originally,
however i lived in US for couple of year during the last 10yr period,

can someone guide me on how to get clearance certificate from US and if it is really manadatory to get my visa approved?

i am given 28days to submit the required documents. i am really not sure how i can get the required clearence from other country.

Thanks for your help

Rgds
Krish