OK, once I got a moment to look the site over - I went directly to the sub-nav:

cURL="http://www.travelsupermarket.com/c/cheap-car-hire"

Opened IE and navigated, then called

oIE.Document.Body.GetElementsByTagName("SELECT").Item(0).SelectedIndex=4
oIE.Document.Body.GetElementsByTagName("SELECT").Item(0).FireEvent("onchang e")

which pulled up USA. The tricky part is that once 'fired' the airport drop down is re-configured for US airports, so you need to decide what airport then set the selectedindex to looking up the array element in the SELECT that corresponds to what you are after.