Your only option right now is to call every day and hope for a cancellation. You really waited way too long to try to get into the Castle to eat. Most people call right at the 180 day mark. The Castle is very popular and is hard to get if you don't call right away.
There are numerous other character meals all over WDW. Go over to allearsnet.com and check out dining and character meals. There is at least one other Princess meal at Epcot and there might be something like it at the Grand Floridan (not sure).