It always puzzles me why people refer to the AF assist lamp as 'infrared'. By definition, you can't see infrared light. If you're seeing the red light, it's red
, not infra
The only infrared system in use is Canon's optical triggering system for off-camera flash. The receiver for that system sees only IR light (the 'window' is black), and the ST-E2 transmitter has the same type of xenon flash tube used in Speedlites, but it's behind a filter that blocks the visible light output. Of course, regular flashes used as a master use the main tube for the optical triggering, so you do see that light.
Back to the AF assist issue, you don't want to use an IR flashlight for focus assist. Lenses have an infrared focusing mark to the right of the main index mark on the distance window/scale because IR light is focused differently. Using IR illumination to achieve focus means that the visible light – the light your sensor is going to capture – is going to be out of focus.
Your best bet might be a bright red LED flashlight, but that still might be too distracting to the riders.
Yongnuo's YN-E3-RT has built-in focus-assist beam, and is the size of the Canon ST-E3-RT. Might just suit your bill,
Alternatively and for less $$, Yongnuo has the YN12AF
, which is simply a standalone AF assist lamp. But...Jim is looking for something good out to ~100'/30 m. The YN12AF is good to 12 m, the YN-E3-RT's distance isn't specified from what I can tell, but I'm sure it won't work out to 30 m.