I can't help you find these items but I do use the Ilford Multigrade 500 H head on my De Veres. In my experience, and it is all I use, the 4x5 mixing box covers the 6x9, 6x7, 6x6, 6x45 and 35mm formats. OK, it would be nice to have all the boxes and plates but in reality the 4x5 ones should suffice. My advice would be to locate the 4x5 ones first and collect the others as and when they present themselves. Unfortunately these items are now becoming hard to find and quite expensive.
The aim of art is to represent not the outward appearance of things, but their inward significance.