In my home town, I practically was the only person buying postcards… I found super old ones at the kiosk! They were the only viewcards of the town until a year later the town info had new ones printed. And also yes to flea markets and recycling/charity stores!
Yes, Libraries have donated books for sale. Once in awhile you can find postcards in the bin.
PS all libraries have book sales: community coll and universities! Contact FRIENDS OF LIBRARY
Touché! Who ‘d think of postcards and beer?
The so-called Edcards in Germany are very good (most of the times), here are my favorite places to buy cards:
Art Galleries (Tate Modern/Britain & National (Portrait) Gallery are great)
Stores with nice papeterie
Are you in London?
and of course Paperchase
MAGMA have a shop near me, will look at postcards there. Paperchase didn’t survive covid lockdown and is no longer.
Post offices, definitely
I have never seen postcards in the post office. I buy them at gift shops, specialty salons or flea markets, but if I ever see a postcard in the post office, I would be very surprised.