Shari,
I found the best price here when I looked last year.
www.TCBulk.com
I bought Golden Age comic book Backing Board - Pack of 100 boards (MH:GOLDENSBS-PACK)
Size 7 1/2 X 10 1/2
Fits Golden Age sized comic bags
Also available by the full case at an even better price per pack
ope that helps
Dawn227
Rochester NY