If you have a neighborhood hardware store nearby, they might have something that would work. My local hardware has all sorts of specialty fittings like that. The color and style may not be a perfect match, but I think the threads are fairly standardized.

These are from Quorum. Similar but a little less inside the globe

I’m not sure why but the photo is being stretched making the drum portion look shorter than it is. The drum is not this narrow

These are called bell jars, not sure who makes these but there is a plethora on the market, not a cheap fixture.