What is the Collective nouns for postcards?

There isn't a widely accepted collective noun specifically for postcards. However, here are a few options you could use, depending on the context:

Formal:

* Collection of postcards

* Set of postcards

Informal:

* Pile of postcards

* Stack of postcards

* Bunch of postcards

* Pack of postcards

More creative:

* Album of postcards (if they are in an album)

* Gallery of postcards (if they are displayed)

* Treasury of postcards (if they are valuable)

Ultimately, the best collective noun to use will depend on the specific situation.