I used and I liked a lot the Thermoscientific (ex fermentas) protein ladders, they are a little expensive but very good. I do not use low molecular weight ladder, only a standard ladder, so I find for you this link on Thermoscientific site:
Its difficult to get the protein molecular weight marker in range of 2-20 KDa from market. i can suggest you one marker from NEB Protein Marker, Broad Range (2-212 kDa)..might be useful for you.