I just bought mine off Amazon, 100 for $11.85. I don’t have any idea where a comic book store is and yes, could probably find one, but the convenience of them being delivered to my door is worth the $1.85 difference to me.
The “Golden Age” sized ones are 7 1/2 x 10 1/2 which is the size that works well for me for yardage and cutting some in half for a yard or less.