I can't remember how I got them in my spare parts box
If you want more, they are usually called grub screws or set screws. For blind hole blanking it's probably best to get flat points https://www.accu.co.uk/en/flat-point-set-screws/152460-SSF-M5-6-A4-BL
How would you get those headless screws in and, more importantly, out?
Magnets
I hope you're not a bike mechanic!
@Tijmen started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
If you want more, they are usually called grub screws or set screws. For blind hole blanking it's probably best to get flat points
https://www.accu.co.uk/en/flat-point-set-screws/152460-SSF-M5-6-A4-BL