I know they sell cotton-poly broadcloth, but the process of making it is different and it is not "truly" broadcloth as a result. I did not mean to imply that it was not on the market. Sorry.
From wiseGeek
http://www.wisegeek.com/what-is-broadcloth.htm
"To make broadcloth, an extra-wide loom is used. The cloth is tightly woven before being dipped in water while being stretched on tenters, special racks which keep up the tension in the fabric. The water leads the wool to shrink when it is pulled out to dry. Next, the broadcloth is rubbed with fullers earth, and beaten with a wooden hammer. The result is a soft, almost felted cloth which is supple, smooth, and very soft. It is also not greasy, which sets it apart from many other wool products.
While wool is the traditional material for broadcloth, cotton broadcloth is also manufactured. Some cotton broadcloth has a very narrow, subtle rib, causing it to resemble poplin, another densely woven textile.
Synthetic fibers are not generally used to make broadcloth, because they do not behave like wool and cotton do when the fabric is specially treated. A cotton broadcloth is much lighter than a woolen, although it has the same sturdy properties." (my emphasis)