https://www.amazon.com/Mayhew-Tools-24001-Center-32-4mm/dp/B00AED3MPI personally that's what i use, but just about any center punch should work.
All you're doing is displacing metal from the end plate into the notch in the castle nut to prevent it from backing out from vibration, same concept as many axle nuts on cars.
Just do it yourself!
https://www.amazon.com/Mayhew-MA24001-MA415-5-Punch-Centre/dp/B00AED3MPI