Calipers use two hard lines on them, which i am sure you are aware.
The repop manufacturers sell both of them in their package.
That's the only way they are sold, as far as i know
I used to buy from Fine Lines, all the time, when i was rebuilding these brakes.
Cost was $35.00, and may still be the same.
You get all 4 of the lines, to do both calipers.