Specular maps are something that tend to be missing, or were poorly made in a lot of Poser products. Personally, I think it makes more sense on skin, hair, and props than on clothing, though. Character renders rarely look realistic without a decent specular map, because the human skin doesn't shine the same way everywhere, and lips always need special treatment to look right.
Unfortunately, the majority of the Poser character textures I have don't have any specular maps, or those were created by simply desaturating the diffuse map. In short, good specular maps are rare nowadays.