Hi,
I was never able to track down a bulb that was specifically called a "c26" (as one poster said, it may not exist). However, I did find a bulb that works at
www.lightbulbsrus.com . It wasn't listed on their website. I tracked it down by emailing them. For reference, the replacement bulb (i.e., the glass part of it) has the same diameter as the old bulb I pulled out of the ceiling fan. The length of the replacement bulb is a bit longer than the old one, but is not a problem. The diameter was the limiting factor. When I tried to use a bulb with a larger diameter, the bulb would bump up against some metal in the housing. This narrower bulb does not.
Thanks again for the suggestions.