Hi Pam,
Character Dining is extremely popular and as Guests are able to make advance dining reservations up to 180 days prior to their visit, these restaurants do get booked up.
I have just tried searching for availability at all Character Dining locations on the Resort monorail for the 24th and 25th September and like you, couldn't find a single opening.
My best advice to you would be to keep checking the online dining reservation system frequently between now and the date of your trip as cancellations do occur particularly with the
Credit Card Guarantee Policy now being in force.
If you still don't have any luck then be sure to try again when you arrive at Disney's Grand Floridian Resort & Spa and as a last resort, you could always try walking up to 1900 Park Fare each day and asking if there are any available reservations.
Don't give up hope - you never know you might be lucky.
Wishing you a magical trip filled with memories which will last a lifetime!