The Sinclair ZX81/TS1000 keyboard was widely acknowledged as one of the more challenging aspects of using the computer. As a result, many commercial keyboard replacements were available in the UK and US. A number of the replacements available in the US were imported from the UK, like the dk’Tronics keyboard.
The E-Z Key and Suntronics keyboards were two notable US-based replacements.
And then there were the many do-it-yourself solutions. Because the computer, and its keyboard, were so simple, it was easy to adapt many other keyboards to work with the ZX81/TS1000. The TI 99/4A keyboard, which was available at Radio Shack, was very popular because it was similar in size and had exposed solder pins. Radio Shack also sold an Oric Atmos keyboard for a brief time, which at least one enterprising user stuffed in the TS 1050 carrying case.
TS 1500 with TI 99/4A keyboard 
TS 1050 with Oric keyboard
