Right, a quick search tells me he's the
CM of the Mortifactors. Info like that will help people- not everyone knows every character in
40k.
Now, there is a a quite simple solution but it requires you to go out the
GW sphere-
This guy from Artel would be a good start.
However to be a bit more accurate as his armour is made
of bone you'll need to cast the net out some more, perhaps get someone to do a custom sculpt as there is nothing in the current
GW range that looks like that. There are some old Chaos champions but they would be out of scale.
EDIT- thinking outside the box a bit further- I daresay Maugan Ra might be a good base. You'll need to do a lot of conversion work, but the ribcage armour is exactly what he has.