You can buy a code from your local online marketplace or you can buy the game. Gamefly doesn't supply online codes with rentals. And nobody on this forum will give you a code for free, 'cuz, you know...yeah.
You must purchase it - it's Ubisoft'd Uplay Passport. You can either buy the game new, buy it through the gamefly 'keep it' option or buy a pass from ubi using the console (they run 10USD) or use the two day free trial. Uplay's FAQ [ http://uplay.ubi.com/en-US/passport ]