There are several members here that have lawnmowers but I think the suggestion was intended to highlight that the Old Lawnmower Club may yield a better chance of success.
Re posting on their forum you do need to sign up for forum membership but you are not required to be a club member, although that can be arranged should you wish to join up later on. As a forum only member you will not have full access to some areas of the OLC Website that are only accessed by full club members.
Re your Atco mower my first thought was that it is one of the Lightweight series but it does not look like the mower shown in the OLC’S Mower Profiles.