Yes, I am not surprised about the limited availability at both of these restaurants. BOG is the hardest reservation in WDW, add to that, during September the Halloween party occurs many nights. On these nights, BOG is only open for dinner for a few hours as it is not open during the party. Or at Least that is how it was at Christmas, the only holiday it has been open for so far.
Obama is usually hard to get but I'm not sure that hard. I would keep checking for that one for a cancelation, and consider BOG for lunch, not as fancy but still a great experience and you get in the castle. Enough to melt any kids heart. Lunch was very tasty and a great experience. I recommend not lining up with everyone else when the park opens, I went at 130 and waited only 15 minutes