As far as I know, the only place you're going to get those tubes, is from another set of carbs! Good luck getting them out undamaged though! (Sorry!)
I think making up some yourself, and epoxying them in place is going to be your best bet. Hopefully someone has a set of carbs on the bench that they can take a measurement from for you... I'm afraid all my spares (which included a couple of sets of F3 carbs) were sold last year, so I can't help any further.
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Andy.
NSR-WORLD.COM
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