I have the original bolts for those covers. Make sure the nut inside is still seated in the plastic. It may not be stripped and if you can get behind it you may be able to save the day.
As for the pillion bolt, I believe it's a 6 x 1.0. Mine "stripped out" once and I was able to re-tap the hole and go again. The next time I took it apart it seemed too shaky to try again so I threaded a bolt up thru from the bottom and put a chrome acorn nut on the top side.
