20-25 kHz transducers
 

Hi to all.
I'm working on a position tracker that uses ultrasonic transducersfor a
program by my university.
According to my plans it should work with ultrasounds of about 20-25kHz.
However, I am having difficulty finding the microphones/speakers I need for
that kind of frequency.
I know that components like these were used in early car alarms but can't be
found anymore.
Can anyone point out a site or a store that might carry such stuff?
Thanks!

i think the keyword is ceramic (speaker/mike)