Family Heirloom Weavers recently wove us up some proper 28 1/2" U.S. Army cotton drill, complete with the period return selvedges.  It makes putting together a shelter half kit a bit easier!
If you can sew and want to save a little money, grab a shelter half kit to stitch up.  These copies of a Hansell contract tent can be done entirely by hand as per some of Hansell's surviving originals, so you don't even need a sewing machine.
The kit comes with everything you need including pre cut pieces, buttons, thread, rope, directions, and shipping to you.