You can practically get your self unlimited 48 hour codes if your willing to spend 5-10 mins doing so.
1) Download the Monster Hunter Frontier App
(or if you have a Japanese profile find it on the dashboard and go to #3)
2) Inject in to your USB memory stick
3) Load the Monster Hunter Frontier App from the dashboard
4) Enter the captcha, if you cant read Japanese use this guide to translate the symbols in to numbers: http://img534.images...82/captchai.jpg
5) Enter the translated numbers you got with the onscreen keyboard e.g. 12345
6) You'll see "Xbox LIVE 48" and that's the code you will use to have Xbox LIVE access for 48 hours.
7) Redeem the code and you're good to go
You can do this once per profile, however you can just create another silver account and get another code to use on your main profile.