If your OSX Client isn't working, before using an older version, try heading to the Steam community forum and see if there are others with the same issue. Usage of a pirated Steam client is against the Steam user agreement and cause problems for you as the user, the least of which is the permanent banning of your Steam Account as well as being banned from any games which uses the Steam VAC. With that being said, unless you want to block Steam from checking its servers for a new update, this will almost always involve the usage of a pirated Steam client. However, it's REALLY not recommended to do so. There are sites out there like FileHippo or that will let you download the older versions of the Steam client.