I definately find more availability by calling. I have seen them offered online, but have been able to get an agent to help me by checking other dates around mine. Sometimes just 1 day out of 5 is causing the problem and an agent can see that.

FWIW, try not to pick dates that cross over a weekend (Thursday-Tuesday for example). The time shares are booked in weeklong increments with mostly Sat and Sun checkins. If you try a Thurs-Tues, you are taking from 2 weeks of inventory and lessen your chances of finding a room. Your best bets are stays that start or end Saturday or Sunday.

This all being said, I think the MVCI are some of the best value for points out there.