I found it listed online at
theaudio.co (The Audio Company). I've bought from them a few times before and they are great people to deal with.
Did you also look into building a Roon ROCK? A Roon Nucleus is basically an Intel NUC board with an SSD and RAM, in a really nice fanless chassis.
The Nucleus would lighten your wallet by a figure a bit north of 1.5L. Building a ROCK with an 8th Gen Intel i5 NUC kit, a 250GB m.2 drive and 8GB of RAM would cost you something between 29K and 32K.
Roon themselves provide detailed instructions on how to build a Roon Rock with a commercially available Intel NUC Kit. A ROCK would run the same OS the Nucleus runs, and would work headless. Setting one up is not very hard to do, from what I can see.
I'm planning to build a ROCK with an i5 NUC in a month or so.
Edit: Your post pushed me over the fence, heh heh. I ordered an Intel i5 NUC kit, a 240GB m.2 SSD and 8GB RAM just now. It looks like I'll be building a Roon ROCK over this weekend, if everything gets delivered by Saturday.