Glen Goodwin wrote:
  At this late date it would probably be easier to
design
 and build an interface so that a common PS/2-type keyboard
 could be used, along with some self-adhesive key-top stickers. 
 Seems like overkill - the interface would need more processor power than
 the ZX81, most likely.  There *must* be a company that makes membrane
 keyboards, and will do a shortish run.  I'd certainly donate a
 working-ish keyboard to get some made up... 
Actually, ZXTEAM already has a fairly simple interface for attaching
an AT keyboard.  The technical details are here: