I personally don't know who makes revolvers in 40 S&W. But I'd look at a S&W 340 in 357 mag. Its got all the features you're after other than the caliber. Small, light (only 12 oz), no external hammer, and easily concealable. My wife's uncle carries one in his coat pocket and says it so light he can forget its there. Also pretty accurate although he did have to add some better grips to get his groups to where he wanted them.