How do you buy premium cylinders?

I'm on the last chapter in the game, have maxxed my salvage rank and dev level for every city (except one). I can't seem to find a place to buy premium cylinders. I've heard that they can be bought before the last chapter and not at an A rank salvager too. It seems the common denominator is that you stop being able to buy them at some point, but I can't confirm that since I've never been able to.

How do you buy premium cylinders?

Solution 1:

According to this thread, premium cylinders may randomly appear once you visit cylinder shop (long rest may be required).

Update:

I've actually got them by myself. Same as in thread above - just long-rest in Torigoth until you get them in cylinder shop. Seems to be completely random - previous time I haven't got them for 1 hour of long resting, and now I did less than 10 times to get this. Screen as proof:

Solution 2:

It looks like the Expansion Pass adds a way to craft them.

First, you have to do the "M.I.A. Nopon" quest which starts in Uraya.

Next, bring 4 Gold Cylinders, 2 Silver Cylinders, and a Chain of Keys (salvaged in Gormott) to Budada in Goldmouth (on the flight deck level).

source

Solution 3:

I've beaten the game, maxed all development levels, and gotten my salvager rank to A, and now they appear at every shop all the time. When I was at salvager rank B, I never saw a single shop with them.