I've seen one or two motherboard/CPU combos pop up on eBay, never for more than a few days at a time. The CPUs are readily available, frequently for rates that make me seriously contemplate snagging another motherboard... until I look back and see how high the prices have risen. Oi. I love my Blackbird and use it every day, to the point that it's become my main machine unless I run into something it literally can't do, but I couldn't rationalize getting another one now.
It would not be surprising to see Blackbirds and Talos boards become more available with time - ARM workstation motherboards are becoming more abundant and performant, the platform is aging, RISC-V keeps threatening to grow into more than a cargo cult that'll re-order the embedded market. But nobody's getting mine.