I haven't found a single one. There is a nice online resource (
http://www.tunisia-stamps.tn/index.htm) but I suspect the nearest physical stamp shops are across the water in France or Italy. I moved here from Cairo and, if there were any stamps shops there, they have all disappeared. We have just gone through elections much more peacefully than happened in Egypt when I was there, and it seems there is a genuine hunger for democracy and "getting the country back on its feet." Let's see what 2015 will bring.