AFAIK Aruba 5400R zl2 comes with Rack Mounting Kit...at least ours all came with Rack Mounting Kits and I never worried about separately ordering them.
Plus, from an (old) installation guide, this reference:
The 5400R zl2 switches have the following components shipped with them:
- HP 5400R zl2 Switch Quick Setup Guide and Safety/Regulatory Information
- HP Switches General Safety and Regulatory Information
- One HP 5400R zl2 Management Module (J9827A)
- One HP 5406R zl2 Switch Fan Tray (J9831A) or HP 5412R zl2 Switch Fan Tray (J9832A)
- One HP 5406R zl2 Switch Rack Mounting Kit (5066-3042) or HP 5412R zl2 Switch Rack Mounting Kit (5066-3043)
- Cable Manager Kit (5189-8716)