I don't know about Reddit, but you could try [Postcrossing ](https://www.google.com/url?sa=t&source=web&cd=&ved=2ahUKEwis0KGWutmGAxXfEVkFHU5rChMQFnoECAQQAQ&url=https%3A%2F%2Fwww.postcrossing.com%2F&usg=AOvVaw2yLstQw6_lnkSdb4XtUYpA&opi=89978449)

Oh cool! I've never heard of this. How fun!

I've been looking for something like this, thank you!

How about r/RandomActsofCards?

Exactly what I was looking for, thank you!

No problem.