Found it. Sacramento Vintage Ford (www.vintage-ford.com) has it at $38.00 (part number 13289)

Quoting the ad: "This compact voltage regulator bolts directly to the back of a Ford alternator, converting it to a one wire unit. It elimnates the stock voltage regulator and all its wiring. A single 10 gauge wire is all that's needed to hook up the complete system. This is a proven component having been used for some time in the industrial and farm applications. Regulator can be used with or without charging indicator light. "

Hope this will help you. P.S. it looks like it's no bigger than 3/4" by 1 1/4".