Are you looking for a box specific to Argon? If not, then Drag2Zero (in the UK) makes a similar box for the P5 and Scott Plasma5. I was close to pulling the trigger on the Plasma5 box but didn't because it's expensive. The speedmetrics boxes are a much better deal!
I'm also skeptical of claims like "The placement and shape of the storage box assists with air flow around the frame, improving aerodynamics over no bottle or other non-bespoke storage solutions" when no data is given. D2Z and Simon Smart do all sorts of aero testing, so if the box really is better you'd think they'd publish the data to prove it.
I had a chance to test in the tunnel this spring and adding the Elite Crono on my Plasma5 (size large)
increased drag by 3.6 grams at zero and 5.5 grams at yaw. Maybe it's possible the D2Z box would have smoothed air flow around the frame and actually been better than the bottle alone or having nothing at all in the
triangle, without testing I'll never know. Given that the bottle alone increased drag I'm glad I didn't order the box.