Here a few recommended sutlers:
http://www.lederarsenal.com/
This is the shop of Jan-Henrik from the German Mess. He makes 100% authentic uniforms and equipment in museum quality. He got the best and most authentic rubber ponchos and gum blankets you can get!
http://www.virginiatrading.de/
Elisabeth Stritesky is one of the oldest sutlers in Germany and is selling mainly US import stuff from Fall Creek Sutlery and Regimental Quartermaster. She also makes uniforms herself.
http://www.us-civilwar.de/
German Sutler. Good prices. Most stuff is from Pakistan. They have nearly at every German ACW event their sutler store.
http://www.historische-marketenderei.com/
Another German Sutler. Good prices. Mainly Pakistan stuff.
http://www.sued-west.com/search/wedge_tent
Outdoor shop with good price A-Tents and Flys. (I have my French A-Tent from them)
http://heritage-militaire.com/en/
Good shop in France. They make most uniforms themselves. Equipment is mainly from Pakistan.
https://www.civilwarsutler.co.uk/
Good shop in England with good prices. Most stuff and uniforms are from Pakistan. The early (Volunteer) Hard Box Knapsacks are very good!