I suppose you could send them to a US distributor, like Digikey, they are out your way, yes? In MN?
They are about 500K ohms/foot if you want to make a really big linear potentiometer.
IIRC, they're HDPE and as such easily recyclable. But re-use is definitely better. I'd inquire with the local artists asylum, schools, etc. to see if anyone needs such tubes. Good luck!
I'd be surprised if Digikey wouldn't just reuse them.