They just screw into place so I'd imagine that they can be replaced. I haven't seen the ceramic sockets on their own for sale, but that doesn't mean they aren't out there. I use Bayco brooder lamps from the local farm store (~$8 for a new one) so that's probably where I'd start to look for a replacement socket, in their hardware department. Generally, avoiding the reptile specific brands yields a better (and cheaper) product.
Thank you CooperDragon. I already have a few other domes that I wont be using that have perfectly good Ceramic Sockets, I purchased a used dual mini dome, and one if the cords looks like it was burnt and has wires exposed and the brown ring that goes between the ceramic and metal is crumbling and almost none existent.