OK I have more information for anyone that stumbles across this thread.
The caviot being: this applies to my 2018 Defender HD 10 XT CAB if yours isn't a cab model, it 100% is not the same.
I have found that for the Rear there are a few options because the rear axles are the same as the 2018+ Defender HD10 XMR so the following axles work for the rear and both sides are the same (so x2 if you need both)
Demon PAXL-3067 / 3067HD / 3067XHD (were not in stock at the time of my order Oct 2022)
GSP 4102043 (ordered one to get me going until my Rhino 2.0 comes available)
Rhino 2.0 AX-7-67-R-0-DT-001
Gorilla GA-CDEFXMR-R (Way too much $ for me to get in Canada)
Front right (passenger side)
Demon PAXL-3059 (may never be available again but exists technically)
Gorilla GA-CDEFCAB-FR (Way too much $ for me to get in Canada)
GSP 4102044 (I will have one Monday but we've already confirmed every measurement with the distributor)
FYI I'm pretty sure GSP makes the stock BRP axles but they're much cheaper from GSP (for me at least)
Here's where it gets wierd:
Front Left:
My dealer gave me a GSP 4102050 axle (for a 2020 HD10 XT Cab) and it matches perfectly, seats fully in the diff and measures exactly the same as my stock axle. other than the notch, which isn't necessary and there is no clearance issue with the knuckle.
The GSP 4102045 (for a 2018 Max HD8 is identical and has the step.
This means that we can upgrade 3 of our 4 axles!
I'm not finding anything for the front right that is easy to acquire up here in northern Alberta Canada.