You should have no problem finding NFL fabric, but the NBA and MLB all I have been able to find for a few years now is fleece.
Or do you plan to make your own fabric? I was hoping to find bandanas since I could not find it by the yard, but couldn't even find them. Or you could do a T-shirt quilt if he has some old t-shirts you can have, or maybe you could find some shirts at a thrift store.