Hobby Lobby is always my go to source for knobs. They have a great selection and if you catch them when they are 50% off the prices can't be beat. As I mentioned yesterday I was going to check there for hooks and I found a great anthropology knockoff.
Anthro's version for $20
Hobby Lobby's version (just add a little glossy white spraypaint) for $3 if you catch it on sale, not identical but worth it for the price difference