A more complex ultrasonic sensor

I take it you are no longer interested in measuring the amplitude of the return pulse, just receiving multiple echos.

That can be done with a few, but not all, of the available ultrasonic modules. One example includes the old-fashioned Polaroid modules once used in cameras, which are still available and work astonishingly well: http://www.uoxray.uoregon.edu/polamod/
The modern versions of this module are sold by SensComp: http://www.senscomp.com/