Not local, but I did a little searching and clicking and found this:

http://www.championexoticcarrental.c...car-rental.htm

and this

http://www.rentexoticcars.com/philadelphia.html

The first mentions lots of cars in the text but has no links to them on the web site. Not sure if that's meaningful, but it's worth calling them I would think. The second is from a directory site, and the company's own site doesn't seem to respond right now. There is still a phone number there, though.

If those fail try Hertz. It won't be truly exotic, perhaps, but some stations have more interesting possibilities than others (and not just the standard Volvos and Jags they officially offer). I would call the PHL station directly (although I've heard it's not a particularly good Hertz location for service, so maybe not).