I have a huge collection of postcards - watch Dover Publications for some
nice sets - I also used calendars forever... it wasn't until almost 20 years
of teaching that I was able to order some nice prints for the art room.
As for matching games with postcards - I think I ordered some of my sets of
postcards through the book "Mommy, It's a Renoir" - it is a nice little book
for teachers of youngers -
I love postcards for sorting activities - I introduce an artist by gathering
postcards of their work and some others - kind of play the 'which one
doesn't belong' game... kid's list attributes on blank postcards - we sort
those into groups - (surprise... ends up grouping by elements) and then can
identify styles based on their observations.