Somebody has a linear carriage MNG 15H ?
Could not find exact model you requested but Misumi provides files for free if you can find one that would work for your scenario. Many of them adhere to a specific set of standards.
McMaster Carr also provides 3D models of their components.
If not, ask the company for their CAD files, most companies will give out Step files if you are interested in purchasing the equipment aforementioned.