What hardware do you have? If you have an E Series device that supports analog triggering than you could do this by setting up an analog trigger and use the ATCOUT pin. When setting an analog trigger, the ATCOUT signal will pulse every time the trigger condition is met.
So, you could set up an analog trigger to occur at a certain rising analog level and each time the input signal crosses this value the signal will pulse. This will give you one pulse per period of your waveform. I've included a link to an example program that shows how to view and output the ATCOUT signal from an E Series device.
Using the Analog Trigger Circuitry Output as an External Signal
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3F11F56A4E034080020E74861&p
_node=DZ52308&p_source=External
I hope this helps.
Regards,
Todd D.
NI Applications Engineer