Originally Posted by csport

RBP has shifter housing, https://www.randombikeparts.com/coll...using-gray-new Not sure if you like the color though. Quality wise you cannot go wrong with it.

Or search for "oem jagwire brake shifter" on ebay, it will give many results for a complete basic Jagwire brake/shifter cable and housing kit. These are quite basic (cables are probably galvanized, housing does not have extra lubrication etc.), but overall it costs less than $15 altogether. Changing the cables/housing later is very easy with a flat bar setup as one does not need to re-wrap the bars.

Beware that Shimano has two standards for brake cables: "road" and "mountain".

You may be able to reuse the old housings if you wish to and if they are long enough.

As people said here, never use shifter housing for brakes as it may burst and result in a loss of brakes when you need them the most.