Anything made from a dragon is considered too exotic for a guild-taught skill.

From the Bone Armor Use helpfile:

Skill at Bone Armor Use represents the familiarity and training needed to
get the most protection out of armor made of bone and related materials.
(Dragon bone is a rarer, denser material not taught about in any known
guild.) Bone armor is often bulky, but some guilds prefer it for reasons
of availability or symbolism. This skill boosts the ability of a piece's
ARMOR CLASS to deflect a blow.

And from the Dragon Armor Use helpfile:
Legends persist of adventurers trained in fighting cloaked in the rarest
of armors crafted from the hides and bones of dragons. It is not known where
the teachers of such rare techniques reside, or if any exist at all.

valguarnera@carrionfields.com