Those are not a "Q" cards. These are called "QSL cards".
O don't see any reason one would buy or by some other way collect them. What is your point to do this?
The QSL has value ONLY to the person, to whom it is addressed. It is CONFIRMING a TWO-WAY radio contact between the two particular ham radio stations.
To others these QSL has virtually ZERO value. That is how it works.
I am a HAM RADIO hobyíst 47 years. I know these things