I used to get the longer (the bolt fabric) boards free from
Joann's & Hobby Lobby.
But for the comic backing boards I get the "silver" edition from BCW
(see link in blue below). I always found they where cheaper there.
If you have a LOT of fabric to organize I suggest buying at least 10
bundles (100 boards to a bundle) to get free shipping.
I have a "system" for folding my fabric, so I took about 4 bundles of
boards to FedEx/Kinkos to have them cut 1 was cut in quarters, 1 cut
in half than half cut in half again, 2 cut in half.
BCW