I think v 15 was the last dramatic change, with multiple profiles. After that he kept changing the structure and editing got too confusing for me. I think there actually is a link to Chumby 3.5 version 21 on SF because that was the last compatible with the Classic. I was going to suggest you ask on zurk's forum, but, looks like you already tried.
I could never figure why zurk never kept old versions available. I was satisfied with early versions because they were so "light" and easy to work with, even fun. Unfortunately, I lost some of my finished USBs to hurricane Sandy, but have a C1 v 15 that I just tried for the first time in months, and works fine. I wouldn't sweat getting the later zurkware. There was a utility for the earlier versions that let you go online and converted your channels into 'offline' profiles automatically. For me that was the high point of zurk's system. Unfortunately then he changed the architecture making that obsolete, as well as a nice manual someone had made. I'm not saying he should have stopped developing it, he obviously is really into it. But it would have been nice if he left us a snapshot at that point that we could still use. That's why I'm really hoping Blue Octy gets things up for even a brief time. I'd love to go back and use the ("Francesco's") converter to recover my old channels.
And I'd happily use one of the earliest zurkware versions. I love simple stable apps. Believe it or not, my favorite mp3 player is Winamp 2.81. It doesn't try to "call home" to tell anyone what I'm listening to, or even give me any ads. It's 11 years old and works on my 'new' OS Windows 7.
Sorry for the sentimental off-topic ramble. I guess it's a combination of the holiday night and glancing at those old widgets on my Chumby tonight.