JCP did sell fabric, as did Montgomery wards and sears.
I worked there back in the 70's and bought it there, I'd guess it wasn't the quality we can buy now, as quilting fabric, but it had to ironed if you made clothing, so I'd guess it was pretty much cotton.
In case anyone is interested I have a "cash book" that my mother kept, starting with her honeymoon trip...She bought 6-1/2 yards of percale, yellow. for 12 cents a yard, probably to make curtains. Percale is 100% cotton, 5 yds of yellow print fabric for 13-1/2 cents a yard. The whole honeymoon which included camping, gas food, etc was $55.59. This was 1941...at the time my dad was teaching and paying his father back for a college loan and paid $10 a month...I was born in '42 and the hospital bill was $59.00.