I don't but someone in Germany does! It's a white form -
http://www.heilfastenkur.de/Pyramiden_Glockenblume.shtml

You could try running it through Google translator to get more info.

I can't find any english websites that mention it, but searching for Campanula pyramidalis alba gets lots of hits. I expect a commercial grower would know more but it looks as if that name is not licensed here.