Shimano CB-E110 is a nice coaster brake hub. I think they may be wider than 120, though. Worth looking into.
Where are you located, @
wiston? Fichtel & Sachs made some nice rear hubs if you want to search for something vintage. I have a Duomatic that is a coaster brake and two speed kickback. It is fantastic. They came in 28 hole and 36 hole variations. The 36, which is what I have, can be hard to find - at least in the US.