You can only list eBay USA if you own eBay USA...
(Now that I've had my morning wry smile, I'll answer more seriously.)
To list on eBay USA, go to www.ebay.com and list there.
To list on eBay Australia, it's www.ebay.com.au.
However, as you're registered in Australia, and have sold very few items (and those were more than a year ago), I would suggest that you first of all get used to selling in Australia under the current conditions. Are you registered for Managed Payments? Have you had your ID verified and your bank account verified?
Where are the items that you want to sell located? If they're in Australia, selling on www.eBay.com is really not the way to go about it. Just list on www.ebay.com.au, but set up the item's postage options for international postage (perhaps to the USA only - or at the very least to only specified countries) and your listing should be visible on eBay.com in the same way that items listed on ebay.com that are available for international purchase are visible on ebay.com.au.
