fly cutter advice please

[JAZZCNC]

Try cutwell tools they sell high quality Collet chuck nuts, both standard and balenced as well as slim line nuts. The balanced ones are the notched type thou and will require a matching wrench which they also sell.
Don't know if they deal with public direct or you need an account. I have an account if you want one getting.?

That said why would you want a spare nut.? In over 3yrs I've not come close to wearing out the nuts on these chinese spindles and I must have changed thousands of bits.
If you make sure the inside where the collet seats is clean and clear of crud you'll never have a problem.