Wiring conduit
The aviation-electrical aisle at Lowes or Home Depot has smaller diameter flex conduit, and/but it is split. It even comes in a variety of colors. Automotive stores probably have the same thing.
Another potential 'conduit' is underground sprinkler pipe/hose. It is a smooth (not corregated) thin-wall pvc a bit smaller in diameter (about 1/2" if memory serves me correctly.
McMaster-Carr also has some, but I don't recall the sizes.
Dennis Glaeser
7A