Welcome to the Moms Panel Nicole!
I am so sorry that you haven't been able to get Advanced Dining Reservations (ADRs) at a
character dining location. Don't give up! Keep checking with 407-WDW-DINE, even after you've arrived. You may get lucky and someone may cancel. Some guests start booking ADRs as soon as their 180 day window opens and may cancel as they get closer to their trip and start firming up their plans.
Have you tried Cape May Cafe at Disney's Beach Club Resort? They have a character breakfast buffet that features Minnie, Donald Duck & Goofy in their groovy beach wear. My boys loved seeing them in their colorful attire. This location is great for days you'll be visiting Epcot or Disney's Hollywood Studios. Both are easily accessible by Friendship Boat.
You can also try walking up at any of the character dining locations and checking availability. But if your family consists of little ones who may be disappointed if they don't get it, I'd send an adult ahead to scout it out. You may have better success if you check as breakfast, lunch or dinner is starting. That way you will have a larger time frame to try to get in. If you are unable to get reservations, remind your kids that they can still meet the characters in the parks.
Keep check on reservations & I'll keep my fingers crossed for you. Wishing you minnie magical memories :-) Allison