Whether or not this appears as a requirement on any given program's website, you would be wise to get some shadowing experience.
How do I find a PA to shadow?
There are plenty of local PAs who are willing to allow students to shadow them. If you know of any, go ahead and contact them! If you don't know any PAs in the area, the Pre-Professional office has a short list of contacts to help you find an opportunity in the area.
How much shadowing do I need?
Some. Sorry to be vague, but no school has a really specific requirement. Most programs like to see that you've done it, but only to verify that you really do know what a PA is and what they do. You may also consider shadowing PAs in a couple of different settings and specialties. In general, pre-PA students generally have between 5 and 100 hours of shadowing.
Do shadowing hours count toward hands-on patient care hours?
Sorry, no. It is usually categorized as "health-related" experience. You could try listing it in the hands-on category, but the instructions in CASPA advise against it, and most schools won't count it.