Not specifically for that one, but there's a whole lot of 40.5mm screw in hoods on the 'bay. You could pick one that looks like the original (pic of one here), but I'd go for one a bit longer/skinnier like the one for the Apo-Lanthar here (of course you can't easily tell if it vignettes until after you've put a roll through).
steve gandy at www.cameraquest.com used to have an aluminum hood to replace those crappy Leica folding rubber thingies, but I donno if he still has any in stock.
Thanks for the input. I ordered one from the bay that is essentially solid and cylindrical and one from another source that is vented but slightly shorter.