There are very nice stationery shops out there, but even in the larger cities, there aren't as many of those as there used to be. And, your average discount or department store has a very limited selection of writing materials.
However, the U.S. Postal Service fills in the gap a little bit. They offer quite a few note card sets, postcards, fold-a-note sets and special-stamped envelopes. If they don't have what you want at your local post office, you can order online! The note cards pictured above are the Twentieth-Century Poets Note Card set. They feature beautiful paintings and corresponding Poet stamps. But, there are many other options on the site. Check it out!