There is no such mirroring command (yet).
There is the BongoCopyChain command for copying Hierarchical chains.
When Rhino’s Copy commands is used the links aren’t redirected to the copied items.
Unfortunately BongoCopyChain doesn't redirect the constraints to the copied object. When you apply the command to your scissor-chain apparently the result looks crap, because the new Object 47 (copy of Object 8) is still constrained to Object 9.
When the constraint is edited to Object 43 (the copy of Object 9) things are back to normal.
There is item on the wishlist to add redirecting of constraints via an option in the BongoCopyChain command.
Now the copied chain can be mirrored using Rhino’s Mirror command (Copy=No) of the entire 2nd scissor. You’ll see that that the pivots of the mirrored object are also mirrored (they follow the left-hand-rule instead of the right-hand-rule) but that doesn’t influence their modus operandi.
Now all that remains to be done is to inverse the datum of keyframe 20 of Object 41 (the copy of Object 2) (make it 48 instead of -48). Also maybe you’ll have to put the copied scissor in the exact right place; select the entire mirrored copy and simply apply Rhino’s Move command.
Agreed that a BongoMirrorChain command would be more comfortable – I’ll add it to the wishlist for Bongo 3.0 (inclusive a 'redirect constraints' Option).