Well yes, there's one here that would give you the rough idea.
It's really simple. You'll open one photo, then choose your Crop Tool and set it to 900x900 pixels at 300ppi in the Options Bar. Then you'd crop your photo square.
Then you'd make your new action (called "Brian's Polaroid" or whatever) and start recording. You only need to record two steps and they're both Canvas Size steps:
First, open Canvas size and leave the little square in the middle of the grid of nine squares. Make sure the Background Extension Colour is white, and enter 1000 pixels for both the height and width, then press OK.
Then open Canvas Size again, and this time put the little square at the top of the 9-square grid. Change the height to 1500px and press OK again.
Stop recording.
Voila! That's your action.
Once you've done that, let me know and we'll discuss how to actually use it for all your prints.