Do a search and you'll find a few threads with pics of E1Bs with different E-series compatible tailcaps.
Keep in mind that the "intelligence" for the 2-stage switching is in the head of the E1B. Hence, you should be able to use any clickie E-Series compatible tailcap.
The only tailcap I've run into issues with is a 2-stage McTC twisty. Seems to be a bit of a conflict between the resistor and the E1B head. It lights, sometimes on high, but flickers on low.
Hope this helps!:twothumbs