Mama’s Fish House a magnificent restaurant in Paia, Maui, Hawaii gives out beautiful cards at the hostess desk. Be sure to make a reservation because they are extremely busy, probably because of the free postcards.
Wayfarers Tours gives about five free postcards to each person that goes on its tours. They are based in England but give great walking tours around the world. They even pay the postage for you.
The Carmel Valley Lodge in Carmel Valley, CA has free postcards at the reception desk. Carmel Valley is the country cousin of Carmel by the Sea. It is warmer, more rustic and much more laid back. The Valley Lodge is a dog friendly rural inn that has a great breakfast among other things.
The Ravello Festival a music festival in Ravello, Italy has free postcards at the ticket booth in the main plaza. They gave me a large stack of last year’s cards that didn’t have much space for writing, but they were free.
Mom Tri’s Boathouse, Phuket Island, Thailand has free postcards in the guest rooms that have a preprinted message and enough room for a note. They also pay the postage for you.