I have been dyeing fabric for 10 years and have a great supplier of prepared-for-dyeing cottons.
www.whaleys-bradford.ltd.uk
I don't know if they export to the States. You can send for fabric samples. It may be worth sending an email to enquire.
After trying several fabrics I have settled on the cotton percale, it takes the dye beautifully and is great to sew. It is 100 inches wide and so is economical. The thread count is quite high so I have to use best quality quilting needles in the machine or they blunt quite quickly. I hope you find what you need.
Angela