Hey Marty,
We unfortunately can’t help with process of writing a custom function like this from stem-to-stern, since by its nature it is a customization request outside the scope of support here, but we can definitely offer some advice and it should indeed be possible to build something like this.
The best piece of advice I could recommend is to just head into the core WordPress code itself and look for where these functions are defined. If you do this, you’ll actually be led through a different functions until the actual function where the $in_same_term is used – it’s in the function get_adjacent_post().
You’ll notice the argument for $taxonomy here defaults to ‘category’, so it stands to reason that if you basically duplicate the $in_same_term-related functionality here but make the taxonomy ‘tribe_events_cat’ instead, it should work similarly.
It’s a more complicated customization to make than you might think from the outset, but head into the core code and start piecing things together – if you have a good backup of your site and content before doing so, and some time to play around with this, I’m sure you’ll be able to put something useful together.
Let us know if this helps or if you have further questions or concerns.
Thanks!
George