You can Try those powerfull LED-Chips, which you can get on Ebay and from some other Sellers on the internet.
You can get those as 5W, 10W, 20W, 50W, 100W.
There are also 200W & 500W LED-Chips for visible Light, but i am not sure, if you can get them for IR.
If you feed those LED-Chips with realy Clean DC-Voltage, there should not be any Flicker at all.
I use such 100W-LED-Chips for Visible Light and get no flicker at up to 1200fps (most my Camera can do, i dont have a Chronos yet).
Should work also for IR-Light, just keep your LED cool with proper Cooling and Limit your Current, because driving these Chips with too high current can seriously Damage them.
The only drawback with such a Light-Setup is, that powerfull IR-LEDīs tend to be pretty pricy.
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Also consider building a IR-LED-Panel or Ringlight with smaller LEDīs (Like 5mm LEDs) because you need no Heatsink for most of those and it could maybe also end up being cheaper.
But i dont know, how much Light you want /need and if a reasonable sized LED-Panel or Ringlight would provide enough Light for you.