I found a pic, if that helps:
here.
For the armor, this is a guess, but I would personally basecoat Celestra Grey, layer up to Ulthuan Grey, and use Drakenhof Nightshade *extremely* thinned down (something like 2-to-1 medium to wash) to give it a slight bluish stain and do recess shading for you.
The tabards and stoles just look like straight black and white, honestly. For highlights on the black, I'd lean toward Eshin Grey (a good, neutral grey that's not too bluish or dirty; my go-to for a lot of black highlighting in the Citadel range) with fine highlights done in Dawnstone.
Again, this is just guesswork, but I think it has a chance of working out pretty well. Do you have a test model you could try it out on? Don't use one of your Rubrics until you've got something you like, but literally any model will work to see if the color comes out right.