Hey Gundamentalist,
Unfortunately, uniform information is pretty rare on the web. I got my inspiration from a picture I saw in a museum a while back. I'm not even sure the colors are perfectly on. In general, the State Police during this period tended to go with one of two basic color designs: Khaki or Blue. Maryland is odd in that it sort of combined both.
For a khaki-style uniform, you'd have a dark khaki jacket, light tan shirt with black tie, bloused motorcycle trousers to match (sometimes with a dark olive stripe on the leg), and brown leather belts and boots. The campaign hat is traditionally an olive or brown color, pretty much like what I painted.
The blue uniform is a navy blue jacket, royal or light blue shirt with black tie, royal blue trousers, with either a yellow or black stripe, and black leather belts and boots. For extra "ugh," sometimes the hat is still olive or brown. Otherwise it's dark blue with a gold hat cord.
The nice part is that uniforms changed colors fairly frequently, as different fabrics and styles got more or less popular. There are also 48 states at this point, so your prospective uniform is going to be close to somebody's official reg. If you want a Pete Murray Rule of Thumb, I'd use the blue scheme for the Northeast (New England, New York, Pennsylvania, Delaware), the Midwest east of the Mississippi (Ohio, Illinois, Michigan, Indiana), and the Khaki for the South and West.
Hope this helps.