it needs to be downloaded from another device.. that could be a tablet or desktop computer for example, open a web browser, go to the Google play website, sign into the account for the keyboardless device, install the app there, it will appear on the chosen device.
alternatively, you might already have a keyboard app listed in Google play store app on your device, in 'my apps' >> 'all', scroll through see if a keyboard is there and install it.