As mentioned by Canadian_zuk, a film canister filled with small lead shot and a little graphite works great!
I use number 9 shot. And add some powdered graphite into the shot. Put the cap on, and shake to coat the shot.
I prep a fired case by giving the outside a wipe with a solvant moistened rag, pass a nylon brush through the neck 2-3 times, then dip the case neck into the "shot/graphite".
Neck size, and you will notice very little friction on the expander button as it resizes/expands the neck to final diameter.
I pass the nylon brush through the neck one last time and its complete.
I like using this dry Graphite as it is easy to clean up, (when mixed with the shot in the canister) it ensures that too much graphite isnt left inside the case neck. It applies the graphite nice and evenly.