Your best bet is probably to figure out when they get their ammo shipments and try then.
Always have clean socks.
Here ya go buddy. This oughtta get you going.http://www.gunbot.net/ammo/pistol/357mag/
When I can't find it in the LGS I always go here. Shop it a little cuz the shipping prices vary with different distributors.
you have to watch, because some online stores charge extra to ship ammo now