Hi Eddie,
If it's a Fixed Price item, list it at the UK site with shipping to US. It will automatically appear/search on the US (or any other ship-to country as well as UK).
If it's an Auction item, there is a new Site Visibility upgrade feature (with fee) in Marketing Tools to have the item appear on the US site.
Note, antiquarians or lots on books do have higher allowed shipping rates, but I think my suggestion should work better for you.
Danno