Commercially available SEPARATE ultrasonic transmitter and receiver?

[cosmotcat]

Was just wondering if there is available, any pre-built, quality, SEPARATE ultrasonic transmitter/receivers ... a separate transmitter, with a separate receiver. I see many quality ultrasonic range finders, etc. ... and I've found schematics for building such devices (usually it's the link to the same 10-year old 'ultrasonic switch' schematic) but was wondering if anyone offers just a transmitter, with just an accompanying  receiver.

A simple transmit a pulse and "Yes, I've received the pulse" receiver pair.

I will probably build one using the old schematic, but was wondering if there are any pre-assembled units out there.

[Del]

If the purpose is localization, you could use several cricket motes:

http://www.memsic.com/products/wireless-sensor-networks/wireless-modules.html

http://cricket.csail.mit.edu/

or make something like it:

http://diydrones.com/profiles/blogs/705844:BlogPost:29412

HTH