i found that it was very easy to make my own leaders. i used a lightweight, not stretchable fabric that is very inexpensive. i serged the edges, although sewing a narrow hem would also be acceptable. i sewed a perpendicular line at the center of each leader so i could properly line up the top, back, etc. then i wrote on each leader its position on the frame and how to attach the top, back, etc to that leader. that has been most helpful to me. the size of each leader came with the instructions for my quilt frame.
there are different methods to attach the leaders to the frame... i chose self adhesive velcro. this has worked great for me, but after several years, this self-adhesive glue has failed... so i need to find a way to reattach.