If it's listing in your store, it's also on the "main" site (we call that "being in search". All items are now in search.
If by main site you mean the US site, your listings will have to show that you'll ship them to the USA. You do that by adding the USA as a shipping point in your listings and specifyng a shipping cost.
Imagination will often carry us to worlds that never were. But without it we go nowhere. Carl Sagan