If you're looking for hardware to augment your pocket operator's functionality you've come to the right place. You can use these devices to do more with your pocket operator, get more interesting sounds, and work more efficiently.
p0k3t0's Sync Splitters for Pocket Operator
The p0k3t0 splitter fixes the problems caused by chaining multiple pocket operators. It creates a signal flow from one source to multiple devices in parallel to help you link your Pocket Operators together better.
Buy them at Tindie.
Hanz Tech MIDI adapter
This is an adapter for all 3 generations of Pocket Operators which makes them controllable via MIDI. There are pogo pins on the board which make direct contact with the exposed button pads on the PO to simulate buttons presses by switching the current on and off.
Buy it at Tindie. Get the source code on GitHub.