You can buy replacement Ducati indicators from Hein Gericke shops for 5.95 - this is an exact replacement (probably made in the same factory!) and includes the bulb too. I had a habit of catching them on the wall at the old house!
These are listed in the Gericke catalogue - I think the part number is 22001950 or 22001940 for the lens only (at 1.95 each).
Gericke also do a range of mini indicators that would probably be just as cheap and come in a wide range of applications - threaded end, plain end, etc, etc.
http://www.hein-gericke.com/