You would be refering to a Zahn cup.........or a Ford cup.............or a Din cup.........among others.

In other words there are a number of different cups out there. The Zahn cup is used more in the states than the others but as was said, it isn't cheap. Last I looked at pricing for one, they are running anywhere between $15 and $130 depending on which cup....which size. There are also a number of different size cups. They come in different types/sizes depending on if you're using low, mid or high solids among other things.

If you're just doing airbrush work, you would have to mix up more than you would use just to check the viscosity since you have to fill the cup and time how long it takes for the fluid to drain from the hole in the bottom of the cup.