Mister Muff, thanks for those links.
Sadly neither addresses my particular needs.

What I specifically need is the shirt linked, in BLACK and LARGE or possibly X-LARGE.

I’m sure it must be possible.
Heck I’m sure I’ve seen pics of Mister Matthews hisself wearing one, and I don’t think he’s a medium !

Also, as the OP asked, why not available in EHX’s own merch store ? – I’d rather give my money to the company.