Cetus MKIII Add-on Pack not buyable due to different stock locations

Whenever I try to order the MKIII Add-on Pack from UK stock, I cannot checkout later in the buying process.
The web-shop says: Check if all selected parts are from the same stock location.
And indeed, the Add-on Pack itsself shows up to be in UK stock, but the listed 4 separate parts of the pack show to be in China stock.

What do I have to do to buy this from UK stock?