I mentioned yesterday my new need for a button that's a keyboard that only does Scroll Lock. I put it to the Arduino-loving corners of Google Plus yesteday, and I got a response.
This is the response. And the wonderful thing is that there are only four parts, they're inexpensive, and I'm sure I have at least one of 'em hanging around. Five, if you require LRF compliance.
Don't know that I'll go with yellow, and I might have artistic fun with the enclosure, but looks like this would be a quick and easy project.