Hi Kolin and welcome to the forum,
If you're talking about selling on eBay, then very simple. You just sign into Link hidden: Login to view with your own account login details and post your listing. Then your listing will show on eBay US. This can be done with any international eBay platform, your login will work on anyone.
Just bare in mind when listing a product, the location must be the location where the product itself is, it's not where you yourself are located.