They use IR leds for that. A 300 mW IR led is 99 cents. Is it a 1 mm core plastic fiber with a black plastic jacket? If so, I know what the sender is and they are all over EBAY from time to time.
http://i-fiberoptics.com/fiber-optic-leds.php You probably want the led with the screw on cap that clamps the fiber.
Otherwise the sensor is silicon and any really bright light will do.
Steve
Qui habet Christos, habet Vitam!
I should have rented the space under my name for advertising.
When I still could have...