Where are the rules for Codex Successor Chapter Trappings? I am trying to create an Exorcist character and I can not find where my Chapter Trappings are. Do Codex Successors just not get Chapter Trappings?

I think they draw them based on the chapter they are based on. So if you are running an ultramarines successor just look at those.

The only issue is that the Exorcists have their progenitor hidden. So they do not have a source chapter. Their Gene-Seed is actually from the Grey Knights.

I am going by the rules found in Honour the Chapter for Codex Successor Chapters. I think it is found on page 99.

True enough, though I am not sure about the Grey Knights bit. I was under the impression that was just a rumor. Well perhaps then you should just houserule something fluffy to use. Here is one idea

Remnant of the Trial - All Excorcists are entitled to keep the holy sigil used to fight away the daemonic possession that all exocists must overcome as part of their Initiation rites. This sigil is often worn on a chain attached to the front of the Space Marine's armor. The sigil is usually a Stylized version of their Chapter Sigil, the horned skull, wrought in fine silver. Wearing it is a constant reminder of the battle brothers inner strength and will give him a +10 Bonus to willpower vs any psychic powers or Fear effects coming from Daemonic sources.

I like this. My buddy plays Exorcists in 40k, and his first character is an Exorcist. This will be good for his character.