Hi Andrew!
Thanks for getting in touch with us!
First, please let me note that we are fairly limited in how much support we can give for custom development questions like that.
That said, we always like helping out and at least point users into the right direction as much possible.
To accomplish what you are looking for, I’d suggest you take a look at the image.php template file located at /wp-content/plugins/the-events-calendar-community-events/src/views/community/modules/
That is the template for the event image uploader. Using our Themer’s Guide as a reference, you could remove the image uploader and come up with some custom coding that would show some sort of images selector.
I hope that helps. Let me know if any follow up question.
Best,
Victor