I have designed, and am currently working on, a number of small items for use with this vintage computer - which I spent far too many hours on back in the day!
RS423 to USB adapter for connecting your Beeb to any modern device with a USP port
An individual 5-pin "Domino" DIN plug used for the RS423 connector.
Replica keyboard cable for the BBC Micro. As close as you'll get to the original pattern!