There are numerous sellers on ebay who offer metal lens hoods in many diameters for about $5 - $8 each. Two that come to mind off-hand are: OldEnglishChina (OEC) and HeavyStar. More can be found by searching for filters, lens hoods, step-up rings etc.
For my 40.5mm lens I've gotten 40.5 - 49mm step-up rings and that permits me to use 49mm filters and hoods. If 49mm is too large, then go with a 40.5 - 43 or 46 step-up ring and buy the appropriate hoods and filters.
OEC sells a brand called DKE and I've found their tele-hoods to be very nice. The wide-angle hood I bought is much too wide and covers the rangefinder but will work well on an SLR lens of 20mm focal length or greater. I suppose I could slot the hood so that my rangefinder looks through. Another job for my Dremel Tool? Another hood I have is made of a thicker-walled aluminum but is quite nice. None of them cost me over $7.95 plus a couple of dollars shipping. If bought together, shipping is even cheaper.
They don't carry the big names but they work just as well.
Walker