I went to the Hiwin website and they have a selector program where you can select the carraige type the rail type etc and it will output a solid model in a range of formats. These are 3D models in a range of formats (e.g. step) not dxf which I believe are only 2D line drawings and not what you want.

When I used the Hiwin tool the model it exported was one entity and the carraiges could not be slid around once in the CAD program. I was Ok with that as I used simple surrogate rectangles and cylinders for the design and only added holes and details at the end. Saying this you do need to think about where the bolts will go so they don't clash when you model the holes at the end and have to make changes.

CAD for extrusions are usually on suppliers website but for initial design just use a rectangle with outer dimensions to match a commonly available size.

If you use steel rectangular hollow section in the design make sure you model the outer corner radius as leaving them square makes it look like you can bolt things right up to the edge.