You don't want to link a virtual keyboard to a real keyboard, doing so gets rid of the purpose of the virtual keyboard.
A virtual keyboard is an on screen keyboard made up of sprite objects.
This allows you to control how the user types things into the game.
The Keyboard plugin allows the user to just type using the keyboard that is in their device.
If you use sprites for a font you will have to create an object for each letter. You may want to look up web fonts instead.
https://www.scirra.com/tutorials/236/us ... ext-object
https://www.scirra.com/tutorials/237/ho ... -web-fonts
You can upload the font files into the game, it doesn't need internet access to use them.