Wow, that sucks about NAPA. I do live out in the country and they are old school around here. They still make hydraulic lines for tractors at ours. I like it, but don't know how long that will last.
I'm sure a lot of this varies with store to store. I went to NAPA some time ago to get some 1/8 or 3/16 or 1/4" nylon tube used to be commonly used, we used to sell a LOT of it. It normally uses a sort of specialized compression fitting with an inner sleeve. Used in air brake systems, etc, and of course was common for add-on oil pressure gauges LMFAO!!!
TWO GUYS I ASKED either did not know what I was talking about or "thought" they did not have it. One of the senior guys finally overheard, and sure enough, hid below a dusty shelf, "was some of it." As I recall I did not get the size I wanted, but was able to "sub" something else.
(What I was using this for, at the time, was monitoring two pressure ports on the White Whale III Dodge 2500 automatic, hooked to a deunk refrigeration manifold.........so I could monitor pressure from the driver's seat)