How can I integrate a radar gun?

I am trying to develop an app that can help kids develop throwing skills for sports.   My end objective is to get the throw speed of a baseball into a python or java variable.  Ideally I want to get a radar gun with a USB interface and API.  I'm not a hardware guy so I have some learning to do.  I know that there are plenty of radar guns out there.   but I know nothing about them or how to accomplish this.
Can anyone point me in the right direction here?  What do I need?  How do I make this work?

Here is a modern design Building the rest is non-trivial, but not too hard.

You used to be able to buy the necessary "heart" of a radar gun, which does the bulk of the work for you, the old Mullard CL8960, it contains a Gunn diode to generate uwaves, and a mixing cavity to do the heterodyning.

I can't find any.

Whilst looking around though, its been pointed out that "dual-tech" PIR alarms use microwave systems too, That might be a good place to find at least a short range unit.

Ultrasound works pretty well for this sort of thing too, and I think the transducers are cheaper than they are for actual radar gear.

For both the trick (heterodyning) lies in mixing the reflected, Doppler-shifted, signal, with the original signal. This gives sum and difference frequencies. The difference frequency is proportional to the velocity of the moving object,  and that is of course the physical quantity you wanted to measure.

The link below was the best description I could find of this trick of measuring Doppler signals with ultrasonic transducers:
seandogue7 years ago
Look yee to the right side of the screen. You'll see a list of potential solutions just below your author info panel in the "related" section. I still don't know why they don't automatically punch that window up for an author when a question is posted, right about the time you are asked if you;'re sure. (no offense intended to you codingJoe)