I see the hp 6632B was only recently discontinued. The rackmount kit is Keysight #1CM002A - looks like it could be duplicated if the originals are too expensive.
Here's an idea: One of my neighbours was scrapping his fridge so I grabbed the shelves and standards as they're big enough to hold equipment about the size of the above hp supply. My plan is to attach them to the wall in my shop so I can have rear mounted cantilevered shelves for stacking my test gear.
Cheers,