The Z80 instruction set lives on via the eZ80, Z180 and others which are binary compatible with the original Z80 instruction set. Unfortunately Zilog stopped making the 40 pin DIP package a couple years ago so yeah this specific board will be hard to source. You can still find them on gray market, mostly ones that have been desoldered from existing boards.

Even if you made a version of this board with the footprint changed to the QFP eZ80, it probably wouldn't work because the eZ80 has different memory mapping and clocking differences.

The Z180 has however had its PLCC packages discontinued. Personally, I find SMD CPUs to not be appealing for these sorts of projects, even if the Z180 is a great chip.