Well, it seems that they split it up between ShadingModels.ush and BRDF.ush.
On BRDF you’ll find the three methods defined as functions. I havne’t tried yet but ShadingModels inherit from BRDF so you probably should change the six calls to this function.
float3 Diffuse_OrenNayar( float3 DiffuseColor, float Roughness, float NoV, float NoL, float VoH )
{
float a = Roughness * Roughness;
float s = a;// / ( 1.29 + 0.5 * a );
float s2 = s * s;
float VoL = 2 * VoH * VoH - 1; // double angle identity
float Cosri = VoL - NoV * NoL;
float C1 = 1 - 0.5 * s2 / (s2 + 0.33);
float C2 = 0.45 * s2 / (s2 + 0.09) * Cosri * ( Cosri >= 0 ? rcp( max( NoL, NoV ) ) : 1 );
return DiffuseColor / PI * ( C1 + C2 ) * ( 1 + Roughness * 0.5 );
}