A quick peek at the 3456A parts list shows that both the front and back jack assembly is part #5060-7478. That covers all 5 binding posts.
The 3455A has different part numbers in its parts list, but the on-line parts listing at Keysight shows that 5060-7478 is also used in the 3455A. So who knows.
For single binding posts, some eevblog users have reported that BS-244MN-R (search for it) is a good replacement for HP/Agilent gear. Depending on what's broken, you might be able to use it to rebuild your broken assembly.
I like the idea of swapping the front and back assemblies. Fix the broken jack as best as possible and hide the ugliness in the back.