I guess you are talking about a bib-front shirt like Lt. Col. Custer was so fond of wearing. If you want an accurate period reproduction, I do not advise you to buy ready-made clothes from sutlers - I know there are a handful of good ones out there but most of them are in it to make a profit and don't bother researching how period clothes should be made. Get a pattern and have someone who knows what they're doing custom make it for you. If that is not an option, and you want a period reproduction, make sure you ask the sutler for documentation. If they don't have any, or don't want to share it, don't do business. I want to make it very clear that I am not trying to disparage anyone, but I learned early on not to rely on most sutlers for accurate goods.

If you just want it to wear, just because it's cool, then no big deal - but if you want a wool one, you may have to have it special made anyhow. There is a company called Hand Sewin' Shirts - sorry I don't know their contact info offhand, you can probably search for them on the Web - they are not cheap but the work is very good and I believe they do custom work.