kim...
I got them on amazon, of course
Photo Postcard 4x6 Turn Your Photos Into Post Cards (15 Pack)
by Howard Packaging
they were $5.20 for the package...and I have the prime shipping thing so didn't have the add on of shipping....they seem fine and I just cut them to fit the cards I wanted to send...
I'm sure they would have them at local hobby or craft stores as well...
have fun!
cheers
nina