You would have to make it, I used a 225cfm fan but then you need a air flow meter to measure the flow and then calculate the actual air flow through the box. But you also need to calculate the area of you output spout.
With all the restrictions mine has a flow of about 176cfm.
However if all you want to do is comparison testing then you won't need the flow testing just build the box and use it:)
We have monitors that go up to 10ppm and ones that go to 199ppm.