There are three different types of Galaxy fiber optic lamps that I know of.
Crestworth Galaxy, Fantasia Galaxy, and Cuda Galaxy.
The Cuda Galaxy can use any small sized Fantasia spray and it's base looks VERY similar to a Fantasia Galaxy base.
Unfortunately finding a nice glass spray by itself is extremely hard.
Very rarely do they appear on Ebay and when they do they usually sell for rather large amounts.
I have seen nice Sunburst sprays sell for over $400 by themselves!
Years ago, I found two Mint conditon Fantasia Firefly sprays on Ebay that I paid $250 each for.
The easiest way to find a nice small sized Fantasia spray is to purchase another lamp that already has one.
I have purchased many duplicate lamp models over the years just for their nice sprays!
I think the spray is the most important part of a fiber optic lamp as it determines how nice the lamp will appear.