I think if possible that FFG should put out a book of NPCs from the various Black Library books - who would not want Commisar Cain or Ibram Gaunt in thier game?

Don't think they'd go for that. But hey, that's what fan fiction's about.

Just craft the character the best you can from the material you got and go with it.

Don't forget what time period, and point in their lives it is. You know, at one point Cain doesn't have his robotic fingers, or another character may not be familar with certain enemies at this point in his life yet.