Goodyear makes a gatorback alternator belt - the inner belt. Part # 4050530. Napa also has one. Part # 25-060410. Goodyear is pretty good at $15. OEM part #N3A1-15-908 at $25.
If you see any cracks on the upper and lower sides of the belt, it should be replaced. Bend the belt a bit as it's easier to see cracks that way.
It's very prone to wear when you approach 60-75k mi. The outer belt (PS and AC belt) wears less. If you are replacing the inner belt, you should really replace the outer too if you see any cracks at all.
Make sure you have the belts on at the right tension to avoid damage to alterator, water pump, PS pump etc.