Hey Paul,
As for second-hand shops, I'm sure there must be more, but I can't think of any off the top of my head. The thing is though, is the earthquake that happened two years ago that was pretty devastating to the area. While there continues to be a lot of reconstruction, a lot of smaller businesses did not rebuild afterwards, so I don't know that what was there before is still around (it's been 4 years since I've been there). However, the one good thing about Kumamoto is that the downtown core is pretty compact - it wouldn't take more than a couple of hours (and that's being generous) to explore all of the shopping streets. If there are still any camera stores around, they'll be there.