There is a plugin for QGIS that generates a Curve Number layer for the given Area of Interest within the contiguous United States. It can also download Soil and Land Cover datasets for the same area.

The SCS Curve number is generated through the analysis of Hydrologic Soil Group and NLCD Land Use Code.

These data set are useful for SWMM, HECHMS, and other hydrologic and hydraulic models.