There is now a listing on ebay for hardware that supports ZX80, ZX81 and ZX Spectrum emulators. Search for "zx81 pico". In the next few weeks I hope to port picozx81 to some of the other hardware on sale. I quite like the thought of a Pico in a converted ZX-Spectrum case running as a ZX81

Full disclosure: I've put together the picozx81 emulator, but I do not profit from any sales of this hardware.