if you have to have a new one, and it has to be OEM, hit up the dealerships... you're looking for the A/C condenser fan. Last I heard, they can still get you them.
Might even get lucky and the parts store could order them.
BUT, just about any pusher style fan will work, especially if you have the pig tail and can just wire it in. The car won't know that you got the fan off of a ford at the junkyard.
EDIT: on second thought... it is a 300zx... so maybe it will hate you for installing a ford fan on it. you know how temperamental those bitches can be... just don't let the car know that it came from a ford. lol