Go to your local library and look for books on horses. Books are a great way to get a feel for things.

I agree, it's a good idea to call local stables in your area. Look in the phone book and in the newspaper. Visit local tack/feed stores and see if there is a bulletin board with notices and ads. Asking the feed store workers might be a good idea too.

Here's a stable I found in your town: http://www.haycockstables.com

I don't know if these are lesson barns, but they might be able to point you in the right direction:
Cinnabar Farm Inc - 121 Midway Rd, Perkasie - (215) 453-7700
Windy Willow Farm - 1801 Mill Rd, Perkasie - (215) 822-9899