What are you looking for, specifically?
I don't have a PA set up, because I have no need for it. But the PA speaker's connection to the CB radio is nothing more than a 3.5mm mono headphone jack. You'd just have to run the wire to wherever you want to mount the speaker.
The CB itself that I use is a Cobra 29 LX LE mounted over the rearview mirror:
The jack for the PA speaker is in the back, and could be easily run behind the plastic piece between the sun visors, down the side, to wherever you want.