Update! Two new sets of thick PBT.
1st set is called Classic Black, and is sold on originative.co
2nd set is Imsto Cherry '98 dyesub, IIRC. Acquired these from a trade on r/mm.
I like the Classic Black on this board a tad more than the Imsto. The legends on the black set are very similar to the black HHKB's, where in low lighting they're almost impossible to see. Personally, I love that about the set. Although, part of what makes the Imsto set look so good is how sharp and
bold the dyesub lettering is. And of course, both sets feel remarkable.