Scrooge McDuck does not meet regularly at the US Parks and Resorts. Your best chances for finding him in the US would be at WDW during Christmas season.
In Disneyland Paris Scrooge McDuck can sometimes be found up by the Small World gates and in Frontierland. He can also sometimes be found in the Disneyland Hotel. Rarely he is over in Walt Disney Studios.
Scrooge can also be found often in Toontown in Tokyo Disneyland.