Don't let people sell you flashlights unless they're super cheap and super reliable. :) Especially avoid buying rescue or air defense searchlights - if a product contains the word "rescue" or "defense", its price will cause a jumpscare. Optics isn't a secret art, Wikipedia has all the relevant information - and if you happen to have a solar concentrator with a reasonable focal length, you have a searchlight waiting to happen. :)
Photo taken from 968 meters.
P.S. Just remember: LEDs need to be current-limited and cooled. :)
Sure, you can pick from a whole world of different LEDs, and drivers. But there are also a bunch of cheap headlamps that are small and bright.