The Ohio Collage Society is holding a show of ACEOs in March. The prospectus is on their site here:
http://shirleyendesaxe.typepad.com/ohio_collage_society_news/2010/12/acco-show-at-the-box-prospectus.html
They're calling for ACCOs (Artist Card, Collage Original) but the idea is the same as ACEO: small collages in the size 2.5 x 3.5 inches. See prospectus for details.
Dropoff date is March 8. Show opens March 11.