Siemen Frequency Output card

I was wondering if anyone knows if there is a third party company that has a Siemens s300 Freqeuncy Out card that range from 0 to 10Khz. I am not looking for PWM but just a plain old frequency square wave 50% duty cycle.

Thanks.

there are some "current fo frequency" converters on the market. I can remember PR electronics. So just use a 4-20mA output card from Siemens and a converter.

That current what we have, but we want to eliminate that and just output a frequency.