I remember using a nice power microphone with my mobile cb radio. It was a noise canceling k40 microphone with a magnet on the back of it. It always seemed to work okay and people heard me. I can remember friends with the nice shiny D104 handheld microphone. The only issue with a power microphone in the car was that it tended to pick up alot of noise. I believe that may have been the reason why they came out with the noise canceling microphone. But you know everybody wanted that power to bust through all the people on the cb radio band.
Today you can find quite a few mobile power microphones through Amazon. They all seem pretty popular and have some decent reviews. The other way to go aside from new would be the used power microphones at Ebay. Just make sure to read the reviews on the product and the seller before buying.
If you are interested here is a link Mobile CB Radio Microphones