To me, asking for a deal on MS points is like asking for a discount to exchange currencies. Thats basically what MS points are, a currency conversion... I doubt a bank will give you a deal to trade your American dollar for a Canadian dollar.
Back on topic, the only real "deals" I've ever seen on these are either through GCO as stated in the OP, or last year when pre-ordering Halo 3 from BB and getting a point card for $5 more. I don't recall a TRUE deal on just the card itself.