I'm looking for a source for aninexpensive venturi flow transducer
for an automotive exhaust gas monitoring project.  'Way back in 1980,
I worked for an anesthesia department, and we used such devices to
monitor respiratory flow from anesthetized surgical patients.  
Such transducers would work nicely for this application - the flow
rates we would like to monitor are from about .5 CFM to no more than
10 CFM.  The device we used back then was a hard plastic tube which
plugged into the endotrach tube between the respirator and the balloon
cuff, and had a small flap in the path of the flow, with small
outlets on each side of the flap leading to flexible tubing, which in
turn were connected to an electronic differential pressure transducer.
By knowing the cross-section of the tube, plus the differential
pressure, we were able to calculate the flow.

It is the plastic part, or its contemporary equivalent,
that I'm looking for now.

Thanks for any help you can give me!