@TimmyP, per the first page of this thread, it’s a stereo/dual gang 10k audio taper pot with 25mm long shaft, 9mm bushing diameter, 6mm shaft diameter. An eBay search for a 10k stereo pot brings up a few contenders but, as you say, none shipping from within the US.
Here’s the product page for the original Fly pot (though they don’t seem to be keeping up with the site security certification):
https://tocos.com/products/potentiometers-7-mm-9-mm
Here’s a bourns pot with a 20mm shaft:
https://www.mouser.com/ProductDetail/65 ... K420K103A2
Note that if you source a pot that has a few mm shorter shaft and the knob ends up not having enough to grab on to, you can make up the difference by carefully thinning its mount on the inside of the control cavity with a forstner bit (something I’ve had to do with a few of my Flys after receiving eBay pots that ended up having shorter shafts than was specified in the listing).