I noticed this show of postcard art sent through the mail at a local gallery: https://www.toucanarts.com/postcard-show-1.
Apparently the gallery does this show every year. You could sign up for notifications if you want to submit work to it next year.
Oh, wow. Amazing! 
This is such a great inspiration! Thank you 
Oooh yeah, this is so cool! I will make a note in my calendar for November so I can possibly particioate. Thanks for the heads up @ForeignCorrespondent
Glad you enjoyed it and thanks for sharing with Handmade RR!
Glad you like it and are thinking of submitting, @lovely-weirdo. I’ll keep an eye out for your work.