For an aftermarket upgrade, I'd check with
http://www.levelten.com/
A lot of the old Q guys have been happy with them.
For OEM, check with
http://www.orderinfinitiparts.com. I went to
http://www.infinitiusa.com, and clicked on the parts link at the bottom of the page. This is essentially the same thing as FAST, Nissan's parts lookup software. I searched for what I think matches your car (although I would recommend doing that yourself using your VIN) and came up with P/N 317051NA2A, which was superceded with p/n 317051NA2C.
Put that in at
http://www.orderinfinitiparts.com and got a match for the low low price of $891.78.
Heath