Surely you can buy a cheap one of those from that Argos on New Oxford Street?
Maplin were pretty important to our Physics department in Manchester - we often had to pop down there to the RS Components bit at the back for stuff in the lab.
I feel like that side diminished a bit as they got bigger so I’m not sure if RS is okay but given they are international I guess they are. In fact RS provided me with a UK keyboard for very little money down here in Australia so I am forever a fan of theirs.