you can buy a roll of steel line and rent the double flaring tool or buy pre flanged lengths with the ends on them. 4' is probably the longest length in the pre flared bin so you might have to use couplings if going that route. if you rent the tool just make sure that 1)the cut on the pipe is square and free of burrs 2) the tool is square on the pipe 3)the nuts are on the pipe and in the right direction before doing the second one 4)the line is blown out with the compressor before installing.

once you source your parts you'll be pleased at the ease of changing the lines and will be glad that you broke one.