If you don't mind getting your hands dirty, you could probably make a prototype pretty easily. A battery, some buttons, and a bluefruit[1] should be enough to make one. You would likely need to also write some kind of input translator (Custom android keyboard or so?) to wrap/ convert the value from straight key presses to your combinations (since you want a combination of key presses to give you just one character). 3D print a case, and you're probably all set to go.

I mean, it's likely easier said than done, and would take some time and effort, but it's probably also pretty do-able.

[1]http://www.adafruit.com/blog/2013/09/27/new-product-bluefrui...