Hauss,
The Newer BDR half-shafts could be Backdraft Proprietary. I kinda doubt it though. They look like Audi A3, VW Jetta front half-shafts. But that's "looks".
If you can take one to a large NAPA warehouse and start opening boxes you could possibly find a match.
The Iconic pricing is not too steep honestly for a quality axle though. OEM BMW and Audi factory axles are approx $100-200 more.
Also Iconic (Backdraft) stocks items in a niche market and are not BIG box parts stores like Jegs, Summit, etc... I'd expect them to make some sort of profit on these slow moving items.
You may try The Driveshaft shop also. Their stuff is quality Hi-HP rated. Although Backdraft is not listed on the site they do custom axles as well.
https://www.driveshaftshop.com/kit-car-misc-parts