They're out there. Look at a tire company that sells 29+ tires like Schwalbe. They say their SV 19F tube will fit...
27.5x2.60
27.5x2.80
27.5x3.00
29 x 2.10
29 x 2.25
29 x 2.40
29 x 2.60
29 x 2.80
29 x 3.00
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Genesis 49:16-17
"Well, well!" said Holmes, impatiently. "A good cyclist does not need a high road. The moor is intersected with paths and the moon is at the full."