This style of knob is the most commonly used knob in the Boeing 737 cockpit. As a flight simulator builder myself, I could not find any on the internet, so I designed my own with my limited AutoCad knowledge. I printed at 0.15mm, 20% infill (PLA) and it came out ok for me. Got a 6.8mm diameter hole at the bottom and holes for two M3 grub screws. Hope it is useful to someone.
More info on my 737 project: https://www.facebook.com/sum1els737