Xbox 360: How do I get a 1 महीना subscription to Xbox live?

I buy the full साल for myself, but im trying to pick up the 1 महीना subscription for my little brother. I went to a couple stores and they only sold the 1 yr subscription. The guy at the store कहा that I can only get a 1 yr through retail. He कहा for a 1 या 3 महीना subscription i have to pay for it through xbox live. Thats no problem, I have a credit card but i cant find where I buy the subscription, is it in the marketplace? या was this guy at the store just an ass? द्वारा the way, i live in Canada if that makes any difference...