Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4940780.
Some prototype Rhythm Bones I designed in TinkerCAD, and a version with a shaker attachment!
I made the shaker a separate file so it can be printed in a different material if you want. Just wait till the shaker is roughly halfway finished printing and then drop some sand or whatever in the cup mid-print. I used chopped up paperclips.
It maybe ought to be printed at a pretty high infill or else it'll be too light to play very well. On the other hand, you could maybe get some neat resonant properties by messing with the infill amount and pattern.
In playing, I've found that you can hold them either so that the plain bone hits the shaker, or so that it hits above the shaker. Either way produces a different sound.