There are several gun shops in PA within an hour's drive of Philadelphia, but none where there is a reasonable prospect of finding many decent sxs. If you are there over the Feb 10-11 weekend, the Forks of the Delaware Gun Show is in Allentown, PA at the fairgrounds that weekend. It's a pretty large show that usually has a couple of decent dealers in doubles and some other interesting stuff. Less than 2 hours from Phila and probably 1-1/2 from Princeton.
If you wanted to try something different for dinner, you might consider hitting the section of Newark (about 45 minutes from Princeton) called the Ironbound. It's home to a number of quite good Portugese and Spanish restaurants. Worth a trip, but the quantities of food served require that you be ravenous to do the servings justice.
