Zehnmm,
Wecome to the CPF. Your post is not in the right forum, but you'll be catching on soon I'm sure.
You can get an E series cell extender from John at Lighthound.com, I think they run about $25. You'll find may other items there you didn't know you can't live without.
You might also consider posting a want thread in the "Lights/buy" forum, and wait to see if anybody has one to sell.
Good luck, a cell extender is a start to having a Surefire Lego set. Add in an E to C series head adapter, and you can mix and match bodies and heads for the range of C and E series lights.
In fact there is such a Lego set for sale here:
https://www.candlepowerforums.com/threads/101831