Topics discussing meetup cards as well as swap offers and requests can also be found in the DIRECTORY Handmade Cards & Mail Art. I added this topic, too 
Examples:
Meet-up Cards for Swap
New year meet up card
Offer: Meetup Card from last World Postcard Day
**OFFER: PT 2020 official meeting cards**
There are groups for swapping meetup cards in several Round Robins, too. And sometimes, people are just asking to swap a meeting card for another meeting card. So I guess the easiest way would be to attend some meetups of your own. Here’s a topic discussing how to make these cards: Designing Postcrossing Meeting Cards
And How to make a postcard with “postcrossing” logo?