Acquiring a decent lens for the Barnack is gonna be an adventure.
My adventure had three stages:
-The first was getting a Elmar 3.5 from a respectable chap on Ebay. He told me the glass was iffy and he was right. Cleaning the glass solved part of the problem but here were numerous "cleaning" marks. The lens is fine if I use a hood. The hood was hard to find and cost me $80.00 (FISON). To properly adjust the aperture you remove the hood. Don't get your fingers on the glass when you change the aperture!
-The second stage was finding a inexpensive Russian lens from a really questionable source in Russia (for the hell of it). I bought an Industar 50 lens for $20.00 plus shipping. When it arrived 15 days later I found it to be in truly immaculate condition with near perfect glass. It fit the camera perfectly and there are no focus problems. I'm happy! Don't get your fingers on the glass when you change the aperture!
The third stage was buying a Voigtlander 15mm LTM super wide and partially dedicating this lens to the camera. I really like this set up.
So, if I were to do this again, (and I would) I would do it differently; I would find a nice Barnack iiic or iiif. I would then try to find a good lens, perhaps an Elmar 2.8 in LTM (and I wanna have the thing in my hands before I buy it) with the aperture stops on the collar or just see what Voigtlander has that suits.