I'm thinking a radial master cylinder from a bike which uses the blue spot callipers.
Early R1/R6 master cylinders are the same as Fazers apart from having remote reservoirs IIRC - 14mm. As far as an "upgrade" they will be the same as the fzs one really and of a similar age so unless you are after the racier look then I am not sure it would be worth it. I am pretty sure they did go to 16mm on later models (and also radial pull) though which would make a difference in feel.If yours is notchy and needs a lot of pull to start working they sound like they need looking at. If the system is bled correctly seals and diaphragm are good and not over extended then there isn't really much to go wrong barring any damage.I run a 19mm radial one on mine and it is much better than std, less pull and a firmer feel with true one finger braking if you want it.