These guys have tons of Brembo stuff, including the "Goldline" masters, calipers and rotors:
http://www.oppracing.com/
Here is the page for OE brembo front mc's:
http://www.oppracing.com/category/1011-oe-front-brake-master-cylinders/
This one is 1mm smaller than ours, which I believe is 16mm:
http://www.oppracing.com/product_display/30777-brembo-oe-front-brake-master-cylinder-psc15-gold-without-reservoir-wlever49-reg/
If that's still too much, this one has a 13mm piston:
http://www.oppracing.com/product_display/32311-brembo-oe-mc-ps13-black-without-reservoir-wlever50/
You could paint it gold...
They even include blueprint spec sheets on most everything, the one above for example:
http://www.oppracing.com/images/cmsuploads/Brembo/OEM_Schematics/oppracing%2010-5053-53%20brembo.pdf
so you can check to see piston diameters and select one with a smaller bore. They have been a great resource for me with all my reconfigurations, and one customization I haven't shared with the forum yet hehe...