My favorite source for Anderson Power Products:
ROSSPAR
They sponsor FIRST teams in and around the Greater Toronto Area as well, and are based a block away from where I work. The people there are amazing, and I've been known to drop by there on my way home during build season for both connectors and advice.
They carry the vaunted crimping tool for the SB50 series contacts... but recommend soldering them if you don't have a proper crimper. (Fill, melt, dip, release! Works great too!) They would've lent me a crimper, but at the time they'd lent out all their extras.
Also, they were nice enough to inform me why in the past our connectors sometimes wouldn't stay together nicely: There are different contacts for the SB50 connectors with different insertion forces (high detent and low detent). If you mix different types, the result is less than optimal.
-SlimBoJones...
P.S. They have extremely competitive pricing! It's worth calling them to price out what you need, and don't forget to mention you're involved with FIRST robotics!