Replacing Spindle for Record Rotating Rack (for Ultrasonic Cleaner)

I recently set up an ultrasonic cleaner, using a motorized rotating record rack to slowly spin the records through the cleaning solution. The spindle that came with the motor only extends halfway across the tank, and I'd like to replace it with one that goes almost all the way across. The spindle spins off, so it should be easy to replace if I can find the right one.

I got the motor through a Chinese site, so I don't have a good product support chain I can use. I'm sure these spindles are generic and available on the internet, but I'm just not sure where to look. I tried Googling, with little success.

Where would you look for something like this?