You can use ResourceManager.GetObject Method
The GetObject method is used to retrieve non-string resources. These include values that belong to primitive data types such as Int32 or Double, bitmaps (such as a System.Drawing.Bitmap object), or custom serialized objects. Typically, the returned object must be cast (in C#) or converted (in Visual Basic) to an object of the appropriate type.
var bitmap = Properties.Resources.ResourceManager.GetObject("bg0") as Bitmap;
In for loop:
for (int i = 0; i < 6; i++)
{
string bitmapName = "bg" + i;
bmp = Properties.Resources.ResourceManager.GetObject(bitmapName) as Bitmap;
if(bmp != null)
bmp.Save("C:\\Users/Chance Leachman/Desktop/bg" + i + ".bmp");
}