You have to realize two things to get the discount:
1- You have to be part of BMW Club of Canada (or Racing under CASC-ON Touring GT)
2- You have to buy your tires in Canada.
The discount is from Toyo Canada (We talked to the guy during last BMW meeting). So you can't apply it to a sale in USA.
The cheaper place I found for toyo tires in USA was: http://www.bmwwheels.com/bmwwheels_toyo_tires.asp
But by the time you ship and eveyrthing, you don't save that much. (except if you go and get them intalled in the usa...)