Oiran Dochu is a reenactment of a procession from the Edo period (1603-1867) with men and women dressed up in Edo period costumes. The parade ends with a meeting between the tayu (senior most oiran) and her customer.
One of the places where you can definitely catch the Oiran parade daily is at the Edo Wonderland Nikko Edomura (Nikko, Tochigi). The parade starts at around 15:00 on most days but the location changes. Nikko is a popular tourist spot and the Edo Wonderland is easily accessible from Tokyo.
For more: Nikko Edo Wonderland
A list of events where you can see this parade. Please note the dates might vary slightly each year. Check the official websites for latest information.
At the Ichiyo Zakura Matsuri, Tokyo (葉桜まつり 江戸吉原おいらん道中)
At the Bunsui Sakura Matsuri, Niigata (分水桜まつり)
At the Shizuoka Matsuri, Shizuoka (静岡まつり花魁道中)
April 4, 6
Miyazaki Oiran-Dochu, Miyazaki (宮崎おいらん道中)
At the Shakuson Kotan-sai, Saitama (釈尊降誕祭)
At the Shinagawa Shukuba Matsuri, Tokyo (品川神社例大祭)
September 28, 29
At the Osu Daido Chonin Matsuri, Nagoya (大須大道町人祭)
October 14, 15 (second weekend)
At the Oiso Shukuba Matsuri, Kanagawa (大磯宿場まつり)
November 4 (first Sunday)
At the Maruyama Hana Matsuri, Nagasaki (丸山華まつり)
November 10, 11 (second weekend)