I live in center city Philly. One good thing is that Philadelphia barbers are allowed to use straight razors and aren't required to use the ones with replaceable blades. There are plenty of barbers in the city that will do a straight shave, I would recommend Joe at a shop named Groom. He's the owner and recently moved to a slightly larger shop and had to bring on a second barber, Sal. Make sure you have an appointment since they don't take walk-ins. I think he tries to do his shaves earlier in the week because he gets pretty busy toward the weekend. The review says its on Walnut Street, but they moved to 1324 Locust and the new number is 215-545-2626. You might be able to find a few in south philly too.
2008 Best of Philly: Mens Shave
http://http://www.phillymag.com/shopping_style/detail/groom
Groom
Also in Center City, Groom is a thoroughly "now" barbershop that prides itself on classic techniques with modern style. But here, instead of watching sports, guys can get a cut and a shave (hot and cold towels, astringent, the works) while listening to great jazz. Rich mahogany wood and lamp sconces give the whole place a Cary Grant sort of vibe.
Groom, 1315 Walnut St., Philadelphia, 215.545.5070; www.groomphilly.com