Can buy it in stock at any autoparts store.
I have never had a problem picking it up.
Have to ask for it and say how many feet you want. Can buy per foot or get a coil of it.
If the bad brake line has good ends, then I get my length and bends on line then cut the ends off the old line and flare on the new line.
the aluminized copper bends and flares alot easier than steel also.

DO NOT use normal copper from a hardware store, it is to soft, will work but under hard pressure like a emergency stop, can rupture the line.