I don't know what it's called or where to get it.  Any ideas? 

http://pinterest.com/pin/170010954655099024/

I would make it--it's easy.

I made the tree cookie cutter that made the gingerbread tree in my avatar--it's 8" tall.

Gotta be careful with hard switchback angles because the aluminum is so maleable it snaps apart but seriously it's a great way to go. Very empowering.

http://www.coppergifts.com/cookie-cutters/pc/Make-Your-Own-Cookie-Cutter-Kit-p4864.htm

Then you could get the exact correct dimension for your particular cake/s.

http://www.flourconfections.com/venetian-window-cutter-set-designed-lisa-bugeja-p-3900.html

I have Lisa's Venetian Windows cutters and whilst great - they are HEAPS smaller .... or this cake is a 3inch square
 

In general, for difficult to find cookie cutters, there's an outfit (I am not affiliated -- just a satisfied one-time customer) called "Copper Gifts" that will make any cookie cutter you need. They managed to duplicate my mother's worn-out-and-then-thrown-out integral sign cookie cutter, from a plan I drew up from memory.

AWww.glasshousecakes.com

There more expensive

AThat's close to the shape on the cake but not the exact shape if you compare the two

Looks like Marina Sousa's cutters from      http://www.nycake.com/marinasousafancyleurcutterset.aspx

Thank you all for your replies.