650b on Canyons

I picked up a 2020 (or maybe '21?) Aeroad for my wife last week forgetting that 2XS in Canyon means 650b wheels (Reynolds AR58 in this instance), and I'm struggling to even find tubes for the darn thing (in Adelaide). It's currently on GP5000 clinchers which are pretty much brand new.

The best I've come up with so far is Schwalbe SV12b (butyl) with a 40mm valve, needing an extender (I'm assuming that's what's in there currently):
Schwalbe Inner Tube – 650b – SV12b – Northside Cycles

Is there a way to robustly run TPU tubes? RideNow sell 650b tubes in the correct width range, but the longest core is 65mm and I think the cores (in this version at least) aren't removable and the fancier removable version don't come in 650b:

RideNow TPU Inner Tube 650B/27.5" (584 x 22-32C) Black Valve -28g | South Side Distribution

Eventually, it'll need setting up tubeless (as per the other bikes in the household) but it looks as if GP5000 TR don't even come in plain old black in 650b. Does anyone know differently?

Thanks for any/all wisdom in advance. PS – the warning stickers have now been removed!