I'm not sure if ifixit has the hinges in stock, but I have seen the hinges listed on another site, so it is possible to replace them. the repair involves completely disassembling the LCD display/top lid including use of a sharp knife to separate the display bezel. if you need it, I can give you a link to a video guide with more detail on the procedure
one thing - I read somewhere that Apple acknowledges there were problems with these hinges and in some cases were repairing them even if out of warranty, or giving refunds if you already paid for a repair. See [http://support.apple.com/kb/TS2948|this Apple support document]. you said your warranty expired but did you already bring your machine in to them to take a look?