Cap the # of Bookings at the Availability Level

We have a cake-decorating studio where customers can book open studio time to decorate 1 of 20 cake kits (the products). All 20 products use the same availability for open studio time. We need the number of bookings to for any given timeslot (increments of 1 hour) to be capped across all products using that availability. Or maybe group products together and apply only one max attendee limit.