It can't be that hard to just do a small production run every once in a while, given that Zilog fabricated these for 40+ years? And there's a few companies / individuals that specialize in these low demand, veerrry long tail markets.
Sadly Zilog never did a 3.3V (or >20 MHz) version of the good old Z80. Only newer (but not quite 100% compatible) parts like Z180 & eZ80. And if I could dream: I'd like to see such an updated Z80 in some beautiful package. Say, a small PGA with quartz window to see the chip (frit-seal), in a couple of different colored ceramics, gold-plated pins, the works. Then present that @ Z80's 50th anniversary? /dream
I guess we should really applaud the Intel 8080 for starting this, but probably the brilliance of the Z80 was simplifying the external requirements. The 8080 required +5v, -5v and +12v, and I think some external clocking and DRAM refresh, whilst the Z80 was just +5v, and integrated clocking and refresh to get the component count down.
Look at the schematic for the TRS-80 on how they handled the drive.