here is one place to browse and shop, prices are cheap, even with the inflated shipping/handling charges. basically a good link with pictures, and pricing info
another, questionable service, but info/pics/prices
oh yeah, ignore most of what they say about the antennas, No mobile antennas have any 'gain' per se, and seriously a 102" steel whip is just about as good as you can get for a vehicle that has a metal roof and is standing still.
longer antennas are better, BUT a properly mounted, connected and tuned antenna will perform better than a $300 poorly installed antenna.
Personally I recommend a 3-5 ' fiberglass whip for your rear mount.
I run a 5' fiberglass on the rear of my 4runner and it works well.
Tune it, Find someone close with an SWR meter or buy one, ( $10-$30) and use that with the instructions at firestik.com to adjust your antenna to frequency with your radio, and make sure the mount is installe properly ( not shorted), good ground, Decent coax cable.
I use Cheap Radio Shack cable, and then solder the center pins on teh connectors, it works fine but it wont hold up to alot of abrasion like the Higher$$ coax will.