George Gibbs made them although whether they held stock prior to WW11 I can't say.
I believe most were built on the Magnum Mauser action.
A company called "Surrey ???" also made some in 505 Gibbs but I'm not too sure what action.
I know of 4 Original George Gibbs Magnum Mauser 505 Gibbs rifles and that is all I have ever seen or found - not that I've looked too hard - but I believe only about 70 were made pre WWII.