Due to a email of interest I just brought SqCVS back into life.
I changed to MC format and adjusted it slightly to work with 3.9.
Read class comments of CVSClient and CVSRemoteFile for examples.
This version is only verified to work with Squeak 3.9 and unless someone asks me I will stick to supporting 3.9 as of now.
If you wish to use it in versions older than 3.9 I think you should be fine if you install FastSocketStream and use that instead of SocketStream.