Those red wires go to a power source...ignition source is the best way to go (so the gauges come on with ur igniton). The black is earths, and the greens would be to go to the senders......well thats how it would normally be if ya go by colours....but with the way the lights are hooked up, maybe the greens are earth, and the black is to the senders.....there will be something to describe them there. If ya can't work it out, let me know coz we recently pulled a set of those out of our race car so I'll go have a looksy.
As for the senders....maybe look in a Speco catalouge, which Repco would have. They are electrical gauges so make sure u get electrical senders. Mechanical oil psi gauges have an oil line running to the back of the gauge, and the mechanical water temp has a copper line going to the back of the gauges. Electrical ones are legal (which is wat u have there) but mechanical ones are illegal, the reason being if the oil line bursts ur gonna get a face full of oil.