The Maglite add on can be found here:
http://www.inretech.net/

If in vehicle, you have a couple of options.

For example, the UK Light Canon can be put in the trunk or behind the seat, is VERY bright and takes normal cells. However, I wouldn't want to pack it.

The other thing is that most rechargables have chargers which can be wired into the car, or you can simply "plug in" the recharger when you get in the car, and unplug it when you get out. You could also get yourself into a routine where you take the light out of the charger at your home, and place it in the car each day.

Note that the Streamlight 35x lamp module can be installed in the 20x. The 20x is the size that you wanted, so this may be an optimal combo.

Regarding the drop in -- bright, but probably not good for spotting.

-john