MethodInfo methodInfo = typeof(DataGrid).GetMethod("ColAutoResize", BindingFlags.Instance | BindingFlags.NonPublic);
  for (int index =  0 ; index <  2 ; index ++)
   methodInfo.Invoke(dataGrid, new object[]{index});

Dim grid = Me.DataGrid1  ' Ваш DataGrid
Dim colCount = 2  ' Ваше количество столбцов
Dim methodInfo As System.Reflection.MethodInfo
methodInfo = GetType(DataGrid).GetMethod("ColAutoResize", Reflection.BindingFlags.Instance Or Reflection.BindingFlags.NonPublic)
Dim index As Integer =  0 
For index =  0  To colCount -  1 
    methodInfo.Invoke(grid, New Object() {index})
Next