This is an old post, preserved for reference.
The products and services mentioned within are no longer available.
I have added a new option to the Minstrel ZX80 Clone kits and builds, it's own keyboard.
2022 Update: At the time of writing, there are still a few Minstrel 2 (ZX80) and Minstrel 3 (ZX81) kits available from The Future Was 8 bit These have a version of this keyboard built in. They are the Final Edition kits, there are unlikely to be any more.