Woah.. he told you to scout for muskets so soon? LOL usually wool and leather is what you want to get first as that is what defines your impression. The gun is a very expensive purchase and harder to find as most sutlers you will have to order it from specially and take weeks if not months to arrive depending on demand. Blockade runner is a good sutler that Mike, his dad, and myself have been going through. They also have fair costs on Muskets. Just like the restrictions your unit may have on uniform check what restrictions they have on muskets. Some only allow 58 cal, others 69, some mix. Most for safety and simplicity limit to three band rifles. Although if your unit has loaner gear they probably have the least in guns since they are very pricey like i said.
Again check with unit commander for sites they approve for both uniforms and firearms.