I Googled as Little Bill suggested and all I found is that you have been all over the internet with this question. So the buck stops here.
How many fixtures are we talking about? You probably won't find an LED replacement for that small size lamp because it would be cheaper and less work to just replace the fixture with one that is already LED. You likely would have to remove the ballast and starter (if used) and re-wire it for an LED retrofit. You can't just swap out the lamp with an LED replacement.