Where can I find a class (classes) about pest & disease identification and DIY integrated insect control (using only organic/natural solutions)?
I have a few suggestions for you.
Come to the Philadelphia Flower Show (March 2-10) at the Pennsylvania Convention Center. You will get lots and lots of great ideas for your garden. Check the PHS Philadelphia Flower Show website for updates in our Gardeners Studio and our Speakers Series.
Consult The Philadelphia Gardening Guide. This is our online guide for learning where to buy plants, what to grow, how to connect with other gardeners and where to learn more. If you click on the "organizations" tab, there is one listing of local organizations offering gardening classes, lectures and workshops for the adult learner. Local botanical gardens and arboreta offer courses. Look especially at Longwood Garden's offerings.
If you are looking for formal, academic courses, there is another section in The Philadelphia Gardening Guide with links to academic programs and continuing education in horticulture. I suggest you look through the links on this page and visit the web sites of the organizations listed here. Temple Ambler, Delaware Valley College, the University of Delaware and Penn State all have horticulture programs and should offer courses on organic controls.
We have a 10,000 volume gardening library here at PHS in which we house information - books, DVDs and journals - on horticulture for the gardener living in the Mid-Atlantic region, so we have information on your topic. Anyone may use our library. We are open 9-5 M-F. PHS members may borrow books and DVDs through the mail.
See also Penn State's Integrated Pest Management page on its web site as well as other online factsheets from Penn State's Cooperative Extension Service.
Hope this helps you get started.