As a bow ranger, how can I maximize my critical chances?

I'd really like to build a mixed elemental/critical bow ranger (with a huge critical multiplier and, therefore, a high critical chance): it sounds like a nice way to deal great damages. There are several passive to increase the critical multiplier, but I can't find so many to increase the critical chance, which is pretty low with the bows I've found so far (the basic critical chance is 5%).

I've also read several threads about this build on their forum, but most of them are either outdated, either heavily debated.

How can I increase my critical chance ? Gear ? Gems ? Any passives I have missed ?