You would book the MVCI rooms the same as any other hotel. So if you are using Marriott's online reservation tool and not seeing any availability, that probably means there isn't any. Note that the Hawaiian MVCI rooms are some of the most sought after in the timeshare inventory. What that means is that the chances of finding a room using points will be very slim to none. In fact, you may even find it tough to find inventory for a paid stay.

I was lucky enough to be able to use points at both of the Kauai timeshare properties (though not in the same trip), and at the Ko Olina property as well. What I have found is that your best chance of using points at a "high" demand property (like any Marriott in Hawaii) will be to try when they first open. They will not have sold off all the inventory yet. So Marriott still owns a lot of that inventory and will be more likely to allow the use of points. We did this back when the Waiohai and the Ko Olina timeshares both opened and were able to use points on a week at both facilities to make a very nice two-week vacation.