Thanks for the comments guys.
David - I can see you remember the microwriter! I've looked at the infogrip BAT - it would do the job but is pricey. I wondered if there might be a way to emulate this using some keys on a standard board. The infogrip BAT seems the best hardware. The CyKey is cheaper but needs a line of sight to an IR receiver http://www.cykey.co.uk/
. There's also the FrogPad but it's not so ergonomic. There are several gaming keypads http://www.razerzone.com/gb-en/gamin...razer-tartarus
, but none I can see which would support a full keyboard character set, or 'chording'.
Is emulation possible in Linux on the keyboard i.e. have a mode where a chord of key presses is equivalent to a single key press?