We just got back last night...If you want just the milestones they go from 1955-2005 (50 of them * 51 cents each)...If you want the rest there are about another book and a half (70 ish) as well as dimes, quarters and nickels...Most of the places (especially the penny arcade) have change machines. I would bring new pennies though!

Also...at the Town Hall you can pick up a list of where the penny machines are located throughout the park.