There are a couple of them kicking around the Mechanical Keyboard community. This sort of thing: https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRSutzW...

However, you will be able to make a keypad consisting of anywhere between 1 and 16 keys using the TASK software. In fact, you will be able to make a highly functional single key for about £7 using the designs I will be releasing in the shortcut keypad crowdfunding campaign!