You'll need to build one. Design and order a 4layer PCB containing the neccessary voltage regulators, clock generation and means of communication (JTAG, and maybe I²C, RS232 or USB?).

There are already some people running multi-FPGA mining setups. And yes, it does scale fully (~190MH/s per chip, can possibly be optimized even further), and if you also account for the PCB manufacturing and assembly costs, even more than that.