Can you get just the hydro breaks without the master cylinder?
Without the master cylinder the rest of the discbrake system wouldn't work at all. The master cylinder is where the pressure comes from out trough the leads to finally push the pistons against the discpads and the pads closes in on the disc making it harder to turn, all that is controlled by how hard you push the master cylinder, the harder you push the master cylinder, the harder the pistons will push the discpads etc.
If your question was if you already have a master cylinder and just want the discbrakes etc, then i would say i think you will probably be able to use the old master cylinder with the new discsystem, there should not be any problems with that.
Should be able to look at spare parts and get what you want and just not choose the master cylinder, but i do think buying spare parts to cover everything exept master cylinder will be more expensive then to choose a complete set.