It is not possible to craft the Kordovan horse saddle since the 2.5 update due to the feat being removed. The saddle doesn’t appear in the saddle workbench.
Kordovan Saddle is usually unlocked after selecting the Novice Saddle feat. and would show as a feat before the update.
Saddle is not available in either Exiled Lands nor in Siptah. I am playing in a private server.