My P-Series came with one "in the bag" late fall 2019 from LBS.

I didn’t thin to look in the bag. I found a pair of thru axles in the bag with levers. Is that all you need?

Robert Axle Project sells thru axles specifically designed for wheel-on trainers. The DT swiss style ratcheting levers that comes with the P-Series may work with a wheel on trainer, but it'll certainly mar them if that matters to you.

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MS: Exercise Science
Your speed matters a lot, sometimes you need to be very fast, where sometimes you need to breakdown your speed.

 I also bought just what I needed for this exact problem from Robert Axle Project

I found one there. Thank you.

Yes, and change the "socket like adapter thing" on the Kinetic.

For my p-series on a tacx wheel on trainer I used a Kurt Kinetic axle. The axle was a hair long, so I cut it to length.