Well, if you group the whole lot and call the new group
"leftSide", you can then select the group, and do a file>export selection. Then import the exported file so you have two versions of your skinned character's left side. Then just select the groupnode of the imported file, rename it "rightSide" and scale it X axis to -1. There you go. If it does not flip to the correct position, it is because you have not built the left side up from the origin, and therefore the group node pivot is not on the inside edge of the character...i.e. the pivot must be on the belly-button so-to-speak before you flip.
Anyways, I have no idea why you have done it this way....you don't ever skin and weight one side of a character and then create the other. It doesn't work and will kill your animation, and produce a ridiculous skeleton rig. Your rig should all be interconnected with no overlapping joints. Generally, you FINISH the mesh...BOTH SIDES, before you rig it, and you finish the rig before you skin and weight it. There are so many hundreds of reasons for this that I ain't even gonna bother starting on it...just to say simply, be sensible about it and think what is practical and what is not. If you don't know how to do something, find out how, don't just assume the functions don't exist. You can usually create just about anything you want if you go about it in a logical way and do your homework.