Instructions
Realize that "vintage" Mickey Mouse costumes and collectibles are typically defined as dating from 1968 or earlier.
Know Mickey's history and his many incarnations to make your search easier. For example, it helps to know whether you are looking for "Steamboat Willie", the Sorcerer's Apprentice, or either. Also consider variations on the classic Mickey look of red pants and white gloves, since this gives you many more options. For example, look for a Mickey-as-Bandleader vintage costume.
Be patient. Vintage Disney items are sometimes hard to come by, since Disneyphiles are dedicated collectors.
Check out Disney memorabilia websites including "Disney Memorabilia" and the "Phil Sears" websites. They can tell you all the factoids about vintage Mickey Mouse costumes and styles over the years. This information can help you decide which vintage costumes interest you most and where you might find them. Decide how complete a look you want. For example, some costumes may consist only of Mickey's trademark attire and a set of "ears." Others might include a full costume, including a mask like those worn by at the Disney theme parks.
Read blogs posted by collectors of Disney memorabilia, or "Disneyana." They can help you find shops and web sites and other resources that sell Disney costumes and other vintage items. If the blog owner has a forum or accepts emails, ask where you might find a vintage Mickey Mouse costume. Say whether you are looking for a costume sized for a child or an adult, and estimate the size you want. One great Disney memorabilia blog is "Vintage Disney Memorabilia."
Get a guarantee of authenticity for your vintage Mickey Mouse costume, regardless of where you buy it. Ensure that the costume is authentic rather than a realistic replica.