One of our black-cased round ones was broken the first year. As I recall I checked auto parts stores, but eventually picked one up while at BCS, and installed it myself later. A little bracket adaptation was necessary, and the wire leads had different connector types, so I had to adapt, but it was otherwise essentially the same light.
You might remove the light and tape-off and secure the wires if on the road, then take it to auto parts stores for a match. Failing that, do a search online, and check with BCS. My light was integral, e.g. one unitized piece. I think it was $50, which seemed a lot for a small 12v. lamp unit, but it's good quality and heavy, and was the nearest match to the original.
After that, and reading here about how spendy a new headlight was, I had protective film like what's commonly put on our front caps fitted to all the front lenses, including the fog lights. The only issue is the curved headlight film wrinkles over time and dirt gets behind it - but it's better than broken expensive or hard-to-find lenses.
Joel