It’s kinda hard to be in this hobby and not be at least familiar with Kotobukiya. While I’ve always known them primarily as a company that sells figurines, they also sell model kits as well. This includes a whole lineup of generic model kit weapons and accessories, conveniently sold under the sub-brand “M.S.G.”, which of course stands for “Mobile Support Goods”, and couldn’t possibly be hinting at any other thing.
(Just kidding. Of course they’re alluding to Madison Square Garden. And maybe monosodium glutamate too. But nothing else, especially not Mobile Suit Gundam. How dare you imply such a thing)
Anyway, I found one of these M.S.G. accessories when I visited a Hobby Town when I was traveling out of state:
This is basically the off-brand version of the YHI 6ML-79MM Missile Launcher seen being used by the GM Ground Type and others in 08th MS Team:
Which made it a perfect fit for the Master Grade EZ-8.