This is admittedly a lazy post where I show that I haven't done much research.
Whenever I start searching around online, I find tons of smaller companies selling ergo keyboards or parts for keyboards, but they are always very pricey and don't match the layout I want. I quickly give up since it can take long to search store-by-store online.
The keyboard of my dreams has:
All (104) the keys. This means arrow keys and as numpad. I like the layout of my current keyboard (below). I guess this is called a "full keyboard"?
Mechanical and with plenty of clackedy clack in the keys.
Has the "Y" key on the left side of the gap! This is my biggest sticking point. I have realized that I type the "Y" key with my left hand 99% of the time and I don't want to change.
I am also willing to investigate split design keyboards if the "Y" is on the left and a numpad can exist separately which I could put to the right of my mouse. But still I'd prefer that to be attached.
I don't care about RGB or lights or much else. Take it or leave it.
My ergo journey started with similar requirements to yours - specifically including the Y and B keys. Along the way, I learned how important layers are for comfort, ditched QWERTY entirely for Colemak DH, bought a 3D printer, and ended up at 40%. Several years ago, there was a term "1KFH" ("one key from home") people used to describe the amazing amount of comfort they found when they never had to move their fingers more than one key away from home position, nor to move their hands.
I'm not saying you have to change your requirements, now or ever, but I think people who start to make their own ergo keyboards may be subject to this sort of requirements drift, such that if they ever make it to the product phase, their products aren't what they initially expected to be building. And maybe this sort of dynamic is what makes it less likely for the product you are looking for to have been built already.