Guys, one of our local flyers had a crash with a Plus about four months ago. It was sent to one of Yuneec's repair facility's where it sat for several months. Eventually they came clean and told him that they could not repair the Plus as they had no parts, no manuals and no indication of when they would get them. Eventually Yuneec US just sent an entirely new Plus kit. He received and flew it for the first time just yesterday.
Long story short: If you need parts for a Plus, your only hope at the moment are any matching items from a 520. Hopefully this changes sooner rather than later.
If it were me and I needed just the arm, I would source some of the carbon tube stock and repair the arm myself. If I needed to fix the arm and the attaching piece at the base; I would buy an arm for a regular Typhoon as well as the carbon tube because the mounting/folding parts are the same. Only the motors, motor housing and carbon tube length are different on the Plus.