I'd try suppliers like Digikey, Mouser Electronics, etc. most should have many types in stock. If you already have had the shell off, get the make and model # off the fan, if haven,t taken the shell of yet check YouTube for a teardown video of a P4, if the video resolution is good enough you might get the fan info from there. Are you sure it is the fan?
Check to make sure the fan is receiving power, etc, and it spins freely.
A bit more info for you, I looked at a video and found its a Sunon Maglev (5vdc)' I,m on a iPad mini 4 right now, but later on a full sized display I should be able to read the model number.