You dont need a resistor, I think the ones you've seen are for something else, maybe an led.
1n5404's would be good enough for 12v 1.2w, the are actually well oversize, the leads on them are convenient for crimp terms.
You can get diode matrix's from some chandlers, it would however be a whole lot cheaper just making one up for your application, screw 2 lengths of screw term block to some hardboard then fit the diodes inbetween them, you then have a safe platform you can secure, if you like you could hot glue them down too to protect from vibration.
You only need to light up relevent guages, ie if the engine isnt running you'd only need the voltmeter and water tank meter to light up, oil pressure/fuel etc isnt needed.