http://www.ebay.com/itm/Kent-Moore-Brake-Pressure-Tester-Gauge-J-37118-W-Car-Powermaster-III-Impala-Etc-/370972204428?pt=Motors_Automotive_Tools&hash=item565faa9d8c&vxp=mtr
There are several more on ebay at the moment if you search the Kent Moore part number. Appears to be some minor differences in some of them.
edit: Instead of a separate thread, I'll throw this in as well.
http://www.ebay.com/itm/Kent-Moore-J-37117-Pressure-Switch-Socket-/200933951634?pt=Motors_Automotive_Tools&hash=item2ec898c892&vxp=mtr
This is the socket for the PMIII pressure switch. Another handy tool to have for these. Several of these on there at the moment as well.