Try the food court in Pacific Place Mall (aka T&T on 36 st NE). There's a vietnamese sub place that makes the 3-bean-drink.
Don't be deterred by the cups they have under the glass counter - they're there purely for display. They'll make you a new drink when you order.
Pho Pasteur is also a great suggestion. I usually grab one there to accompany my banh mi from Thi Thi.
Is that the Vietnamese dessert drink made with red bean, mung beans, coconut milk and jelly? I like the ones at Pho Pasteur Saigon in Chinatown, across from the government building. They have a layer of green jelly at the bottom, followed by red and mung beans, then shaved or crushed ice, then sweetened coconut milk and you can add dried longan if you like. I've never looked for one elsewhere, so I'm eager to see what other people say!
Pho Pasteur Saigon Restaurant
207 1 St SE, Calgary, AB T2G 2G3, CA