Looking for either "Date Field Popup Widget (Views Filtering)" or "Date Field Reference (with Popup widget)" I've been looking for quite a while, but I can't seem to find a solution in Drupal 7.

Anyone know a module or a method of filtering a date field popup widget, to only allow dates to be selected based on a views filter in the node creation form?

Or a way to reference another date field (possibly via Entity reference) that allows me to still use the date popup widget?

Any help would be much appreciated. Thank you.
Date Restrictions provides restrictions on allowed values based on several criteria. It still doesn't implement filtering by views results, but you may give it a try.