The originals can be had, but they tend to be pretty pricey because they're unique and somewhat rare. Flare with this lens in such situations is well known though and especially if the sun is in the frame. A hood won't help with that - just light entering the lens from oblique angles.
An alternative might be one of the Voigtländer hoods that use the same compression/friction fit. I believe the slip-on size is 43mm though, which is kind of an odd size so you'd need to look at the slower lens' hoods.
As for a regular screw-in hood, the filter thread of 41mm doesn't help much either as that's also a pretty odd size. Though you can get away with a 40.5mm - it won't fit exactly, but will hold well enough and is a more common size.
If you want to get creative, cut up some (black) cardboard and cut it to length so that when wrapped around the lens it's tight...