How do you buy premium cylinders?

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: