For anyone finding this thread; Thule make feet, but they are rebranded Jaguar and only available new from a main dealer.
I found a plentiful supply of XE roof bars (complete with the feet) on sites such as eBay, Facebook Marketplace, etc. and managed to get some feet (sold without bars) to fit my existing Thule bars, from a kind gent up North! No need to buy from Jaguar unless you want to pay about £260 and have them all shiny..