Velvet and velveteen are usually found in a fabric store where dressmaking fabrics are sold. Hancock's and JoAnn's are two chain fabric stores that are commonly found across the US. You can also look at upholstery velvet or velveteen. Both the abovementioned stores sell upholstery fabrics, too. Now, you may ask, what is the difference between the two? Definition from the Dan River Dictionary of Textile Terms: Velvet: A warp pile cloth in which a succession of rows of short cut pile stand so close together as to give and even, uniform surface; appealing in look and with soft hand. First made of all silk, many major fibers are now used in the construction. When the pile is more than 1/8" in height the cloth is then called plush. Velveteen: A filling pile cloth in which the pile is made by cutting an extra set of filling yarns which weave in a float formation and are woven or bound into the back of the material at intervals by weaving over and under one or more warp ends. Usually made of cotton and is washable.
When the time comes that I decide to buy backdrop fabric, I will compare them side by side. That is why it would be better to go to a fabric store where all types are on display.
This is probably more than you wanted to know.
Beverly A.