After much searching, I actually got one from Sally's Beauty Supply. I had read that natural bristle brushes were best, and it seemed like so many of the ones at pet stores were synthetic or a mixture of synthetic/natural. Plus some of them seemed very rough to the touch.
Here is the one I got. You can buy it online, but I got mine in the store: Brush Strokes - Brush Strokes Soft Boar Bristle Brush
. It is specifically labeled as a "soft" boar bristle brush, which I think makes a big difference.