This is actually not too uncommon of an inquiry. Most times, just getting the vehicle out and driving it will solve the issue. Here is why. The oil temperature actually does not climb at the same rate as, say the coolant temperature. Depending on the engine, and the build (tolerances) of the engine, along with many other variables, it is possible to not see an oil temp reading at all if you simply run the car in a shop, or idle the car for a long period.
When you drive the car, and the engine is under load, the oil temp will begin to rise. Again, depending on many variables, and how it is driven, the rate of increase is different from one engine to the next. If driven hard, especially for any length of time, the oil temp may even shoot up beyond water temp. This is also not uncommon.
If, in fact your gauge still does not read after being driven, and even after being driven under heavy load, or driven hard, then check to make sure that your sender is threaded into something that is sufficiently grounded.