Made some progress today.

Measured the wavelength of a couple of Canon AF assist lights.

AF assist light from a Canon 540EZ flash. The wavelength is about 725nm.	AF assist light from a Canon 550EX flash. The wavelength is about 700-715nm.

Now to look for some LEDs in that wavelength.
The other requirement is that the light source needs to be able to handle several hundred mA. (so the 20mA regular LEDs are out of the question)
I did find a 1W 730nm IR emitter at DigiKey that may do the trick. I’ll have to order one and try it out.