Alright, pics to follow later but I'm commuting home atm so I need to occupy myself somehow.
Turns out the McDavid thermal is a bust. While the stitching pattern does match that of the 8840 and 8800, the color (described promisingly as "Charcoal") is more of a medium grey than black. So after fruitlessly searching online for either the 8800 or 8840 in Medium or Large I decided to just go to the source and call McDavid customer support
After a conversation with a very nice customer rep in which I explained why I needed the hex pattern version as opposed to the current M logo pattern I left my name and number. I should hopefully hear from them tomorrow, so until then let's hope that they either have a bunch in stock somewhere, or they at least know of a reseller who may have stock left over...
Oh, and as for the shirt being reproduced at some point in the future? The sad truth is that they're looking to rebrand their hex pattern shirt with the M logo, so chances are we'll never see the screen-accurate shirts in production again
EDIT: As promised, photographic proof of how wrong the color of the thermal is
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On the right is my McDavid 8800R which I had bought because it was listed as a T, but honestly it's a nice shirt so I'm keeping it), and on the left is the thermal.