Existing one's? Do you mean from Nissan?
The 350Z has no oil temperature sender from my knowledge but either way the gauges come with everything you need when you buy them. All run by a Defi controller using Defi sensors/senders.
Link: http://www.driftwork...-bf-gauges.html
If only someone were selling such a set for considerably less than that, like this for example.
I actually just PM'd someone I know on here who's going FI soon to give them the heads up about your sale.
GLWTS and I'm sure they won't hang around for long.