For this particular series of Train Simulators, there is not a large selection of "High Detail" track for narrow gauge applications that are textured(weathered) to Rio Grande spec of maintenance.
Dan, I suggest using a rail+tie track spline and then using a fill spline underneath. The fill could be retextured to a more authentic style and be able to have the height adjusted to fit underneath the rail+tie to either cover the ties in some areas or have it sit underneath just enough to real. Just my 2 cents...