Very ornate Lamp that needs a piece of slag glass

This lamp is something of an Enigma to me. It is 3' 3" tall and is very heavy. The shade has one piece of slag glass that is missing. I would like to replace the glass if I can find someone who has any. The shade is 1 1/2 ' wide and is 16 1/2 " Tall. The piece of slag glass would have to be tapered with measurements of 1 and 7/16" at the top tapering down to 3 and 3/4" at the bottom and would be 13 1/2 " long. There are no markings at all and the bottom is completely felted so no clues there. Any information on this lamp would be most appreciated. This was handed down to me from my grandmother when she moved into the home so I do not know how old it is or where she got it from. I love this lamp and would like to return it to its original condition.