OK, now I'm reminded of library-checkout punched
cards from the 60's.
They were around the same size as the card-catalog cards so as to fit in the
same pocket in the front of the book. The funny thing about them was they
were punched along the edges with some combination of rectangular notches and
round holes, IIRC.
Are those the ones you could 'search' by putting a metal rod through one
hole position in a stack of them and the extracting the cards with a hole
at that position and leaving the ones with a slot behind?
-tony