I would like to know this too, as I live near Philadelphia and go there regularly. Do you have any specific stores? I know of a few.
On Race St., south side of the street, right east of 11th st, there is an underground Asian Supermarket (it's listed on google maps too)...small entrance, easy to miss...the market is underneath a parking garage. This store has a huge selection of teas. They carry Ten Ren and Van Cheong's loose teas, as well as a large number of other brands, many of which are not even labeled in English. This store doesn't carry many Pu-erh's though. It has a better selection of Oolongs.
Same general area, across the street (north side), in a storefront on the first floor, is another smaller supermarket with a totally different selection of loose teas. They sell Foojoy loose teas, which can be hard to find and are of surprisingly good value and quality. I've had mixed experiences with the other teas I've bought from this store, however...I don't think they're as selective about what they stock, even though their selection is smaller. But maybe I just got unlucky or didn't know what to buy?
I haven't found a good place to buy Pu-erh's though! I would be very grateful if anyone had any other places they knew about!