Jumped on another blog posting today: About Beta Readers - Connect With Some Here.
She's a book illustrator, though she's got various posts about writing too. She's trying to put together a site where authors beta read each others books. We'll see how well that plays out. But ...
She also listed several public Beta Reader groups (though some of these charge for the service (of connecting readers & authors)):
1) Beta Readers & Critique Groups | World Literary Cafe
2) Beta Readers' Hub
3) The Circle: for readers/beta readers/critiques/reviews/free …
4) Beta Reader Group Group (4797 Members) - Goodreads