We just got back and lost something at EPCOT as well.
I went to guest relations, and they only keep lost and found items on the day that they are found. After that, it is all sent to a central location.
I was given a card with a phone # to check on the item the next day.
Theme Parks lost and found:
9am - 7pm 7 days a week.
407-824-4245
located in the transportation and ticket center
Good luck!