Hi good2know.
The Juniper SE or your reseller SE is your best contact for the part numbers.
I have done some investigation and the SKUs for EX4550-32F are:
EX4300-UM-BLNK EX4300 blank faceplate for uplink module
EX4200-PWR-BLNK EX 4200 Blank Panel for Power redundant Power supply slot (Spare)
The information was found in configurator tool for Juniper partners.