Material as thin as a drinking straw and as flexible as a latex tube?

[JBA]

The OD of the thin wall brass tubing might be able to fit into the fabric channel and still have an ID large enough to pass the balls and the connected flexible tubing then providing for an ease of loading of the balls.
Go to the below site to see the ranges of diameters and lengths available:
https://www.grainger.com/category/p..._D_BwE:G:s&s_kwcid=AL!2966!3!317451745875!b!g!

 

[Nik_2213]

There's a surprising range of Teflon / PTFE tubing sizes available on eg Amazon, intended to feed 3D printing filament. Although pricey, it is fairly stiff, and may be bought with a kit of connectors. You may need to apply mild suction to load with beads, then a little air-pressure to dispense. A modest aquarium pump may suffice...Um, I have no idea what material is used for 'Intermittent Self Catheterisation' aka 'Enlarged Prostate Stretch', but its combination when 'fresh' of stiffness, mild flexibility and surprising reluctance to squash or kink may approach your need. Downside, each sterile, one-use device becomes remarkably, intractably stiff when the initial lube dries off...