This is similar and in stock, if you’re okay assembling it. They have great build documentation.
https://keeb.io/collections/keyboard-pcbs/products/quefrency...
https://keeb.io/collections/keyboard-pcbs/products/quefrency...
Thanks for this. I'm getting closer to what I'm looking for.
I'm comfortable designing and assembling PCBs but don't really have time to debug a brand-new design, so I've ordered a low-profile Lily58 kit. The Lily58 is most of what I want and has open source PCB, schematic and case. If it doesn't work for me, I'm expecting to modify it to something more like Quefrency.