Shop direct are NOT big group at all, they have Very and littlewoods that's it, one of which is designed purely to screw over people with poor credit, John Lewis on the other hand is one of the biggest retailers in the U.K. So if they're not stocking plus models (because there isn't any) I really doubt anybody will be, funnily enough I know the CLO of John Lewis but never though to ask him about this seen as I though Apple would have enough stock to at least last the initial five minute on Friday
EDIT: Apolgogies he's not the CLO that was his role at ASOS he's head of operations for John Lewis, ironically he was also the GM of Shop Direct about 10 years back
For what it's worth, Marshall Ward a retired Shop Direct brand was 100x worse than Littlewoods with the worst customer service of any retailer I've ever come across to this day.