Here's another sutler who comes from an enthusiastic recommendation and my knowledge of his reputation within the Civil War reenacting community. As of this writing, I've officially covered all the sutlers that I've had dealings with, or know their reputations well enough to blog them.
Tim Bender (or TP&H Trading Company) has a great reputation in the Civil War part of the hobby for making great headgear, and I consider him one of the "big three" of hat makers, next to Dirty Billy and Greg Starbuck. Although he does limit his selection to the 19th Century, he does have a considerable selection. Arguably, for the price, TP&H Co.'s hats are the best quality you can find, and it has been told to me that he is the source for accurate Hardee-style hats.
Please bear in mind his selection seems to be exclusively brimmed or "slouch" hats.
If you know of sutlers or vendors that hold to a high standard of quality and sell great goods, please drop me a comment, and I'll blog them based off your recommendation.