hi,
You can buy self adhesive reflective strip, clean the shaft and adhere the strip along the shaft.
If you want to improvise, use a piece of aluminium kitchen foil.
Depending on the diameter of the shaft and the distance you want to space your detector away from the reflector, you can buy small red or clear reflectors from a local cycle/car shop.
If your shaft rotational speed isn't to high, you can use a small linear permanent magnet on the shaft, operating a reed switch.
Just have a simple RC filter on a +5v system.
Regards
EricG