you can try ebay, or a junkyard...
I know Nissan offers lifetime warranty on seatbelts, but not seat belt motors. I know cause my 240's automatic seatbelts took a shit on me, took it to the dealer, and they told me the motors weren't under warranty. I had parked in the corner, and the guy said "drive it up, we'll take a look." Maybe the angels were smiling upon me that day. I knew it'd cost me a fortune to fix, but luckily the second i sat down and turned the key, they worked again..!
TAKE THAT YOU FUCKING STEALER-SHIP!