There's a very small IG account for Muramasa, no new posts in over a year.
Nothing to be found about Kiwami, other than an account created last week with one post and no followers. This one seems super fishy to me.
Also, the w37 notation might be a translation thing. I've noticed this before, but when searching Yahoo for jeans for jeans by size categories on Buyee will go from w36 to w37.
But when you look at the actual search results in the w37 category there's a bunch of w38, w40, w42, etc., so perhaps it just is meant to house anything larger than w36?
Just guessing here, I know zero Japanese.