These aren't the only things out there of course, but it should get you started and keep your drawing busy. Available in smaller, more digestible chunks at www.htdhorses.com :
Western saddles have a number of different parts that make the saddle both functional and effective. It is important for riders to know the parts of the saddle in order to determine the correct saddle size they need and learn how to tell the different types of western saddles apart.
The Basics of Proper Horse Care
Top tips for choosing a saddle
ubraidit.com ~ Mohair Cinch by Cielo Cinches (https://www.facebook.com/pages/Cielo-Cinches/198331466857978)
The Parts of the Western Saddle and the English Saddle.
ubraidit.com ~ Cinch design by Amy Davis.
Traditional Mohair Cinches: Breast cancer awareness cinch.