I have had some experience with commercial machines and one of the vendors I liked dealing with are these people.
http://www.sewinggold.com/Index.html. They have a good selection and their prices can't be beat. They will ship to you via truck and are very fast to process the order. Maybe one of the new Singer 20U-109 machines would work. 2500 stitches per minute for straight stitch, and 2000 for zig zag. The machines are made in China but come with a domestic warranty from Singer and they are a true commercial machine. The U-20 machines in all of their variations have ben made for years and are the standard of the commercial dual purpose use in the sewing business. If I were going to buy one I would spring for the optional servo industrial motors, as the machine will be a lot easier to handle than the Clutch motor that is usually used on the commercial machine. If you are used to the clutch motor already then that might not be an issue for you and you could save an extra 150 bucks. I wish I had the extra space in my room as I would buy one of these in a minute.
John