Options for fully lined bulk cable housing
You can buy 30 meter rolls of cable housing such as http://www.wiggle.co.uk/transfil-gear-casing-30m-box/ . I would opt for Shimano or Transfil, as have seen problems with the much cheaper Clarkes.

Brake  cable housings  have a completely different construction to shifters. The housing is a coiled sheath , compared to the axial strands in shifter housing. And brake housing is larger diameter. So different housing for different purposes.