Sing magazine was launched in 1954, edited by Eric Winter who was also a singer, as was John Hasted. There must have been a market for the magazine - where did they sell it, where did they perform? -Derek
I don't know about selling the magazine, but the long 3-part article by Alex Easton I mentioned above (over three issues of Tykes' News in 1990) is worth you tracking down. Alex goes into a lot of detail about the early days of the Topic - 1956-7 mainly - and the sources they had for songs, including Sing.
One person he mentions a fair amount is John Hasted (Professor of Physics at London University until 1986, I see, so he must have been busy enough in the day job), who was "guide-animator" for an early "Music for Youth" weekend school The Topic organised (before it even got its name) on 11 November 1956. The article says Hasted drove to Bradford many times, played banjo, guitar, accordion and piano, knew hundreds of songs and tales and had the happy knack of being able to pass on his knowledge in the most genial manner.