The globe you need is 3-1/4" high. A Kopp or Corning globe will work. Here are a few for sale.
http://www.ebay.com/itm/CORNIN...;hash=item4d2de9083b
http://www.ebay.com/itm/Short-...;hash=item3cf2746259
http://www.ebay.com/itm/KOPP-C...;hash=item51c9dff46d