I am uploading my fairly basic sim racing paddle shifter design. Along with .stl files, I am including a .step file for the shifter so you can customize or upgrade as necessary. I used paddles from the following link so I will not upload them here as well. https://www.thingiverse.com/thing:2745297

For each pair of shifter, you will need:

2x 3d printed shifter body

2x 3d printed shifter shaft

2x paddles of your choosing with m3 mounting holes spaced 10mm apart

2x switch (I use the following but you can modify the .step to fit a cheaper microswitch, if desired)
https://www.digikey.com/product-detail/en/crouzet/831810CFD0.0/966-1426-ND/2415867

4x 7/16 inch x 3/16 or 1/4 inch magnets
https://www.kjmagnetics.com/proddetail.asp?prod=D73-N52
https://www.kjmagnetics.com/proddetail.asp?prod=D74-N52

4x m6x10 button head screws (for shaft axis)
https://www.mcmaster.com/92095a224

4x m3x12 socket head screws (for mounting paddle to shaft) can use any size suitable for the paddle thickness you choose to use
https://www.mcmaster.com/91290a117

4x m3 nut (for securing paddle to shaft)
https://www.mcmaster.com/90592a085

4x m3 screws for mounting shifter to button box or plate