[vidguy]

Might be most economical to buy a used harness from a gauge car for the year that you have gauges from.
If you cant do that I'd suggest you get any harness so you have one you can hack up to build one good one out of. You can always fix up the ends as Warbird said, if any are missing but you'll have the plug. The plug that fits into the back of the gauges is different in sizes, even between the years. Sometimes when you buy the gauges guys will have cut the wires but left the plug in. This can be useful for the connectors/wires in the plug.

I did this in my 75 Formula car.
A wire harness, and the connectors, come in handy anyhow.. I bought a few cheap just to have the plastic fittings and the wiring to use here and there.

And yes, as Warbird said, get a diagram. Even the Haynes manual has a pretty good set of wiring diagrams that I used..Although I did need a magnifying glass...