I am wiring my car now so I just wanted to report what I decided. Gas64 (Gary) had a really good idea with hooking the buzzer to the "I" terminal on the voltage regulator but I believe there would be times the buzzer would sound for a just a second or two until
oil pressure built up.
I decided to go with a device called a "delay on make timer" by Amperite. You can adjust the time delay from .1-30 seconds and it will flow 2 amps. This will allow me to start the car and give enough time to build
oil pressure before the buzzer sounds. Then pressure is built and the
oil pressure switch opens (no ground no buzzer). When driving if I lose oil pressure the buzzer will sound after a few seconds. I will then add a switch under the dask to shut the buzzer off if I am working on the car with key on.