1980 kz1000 front brakes

I've been looking around but haven't found the rubber diaphragm that goes inside the front brake fluid resiviour.  
Is this available anywhere or should I just buy new resiviour/brake ? 

Those reservoir diaphragms are out there but pricey. Check out ebay, 2 of them listed. Part # 43028-1002. BUT..make sure the unit operates without leaking first!! These Kawasaki trapezoid Masters are the Worst of all the Tokico units used on many KZ1978-1980 bikes. Problem is they incorporated a "Steel" bore sleeve which often rusted resulting in no pressure or leaking like a faucet. NO rebuild kit will repair/compensate for a bad/pitted piston assy bore.     

You can find those here :

 
 

Thank you guys for the info and direction. 
really appreciate it !
asphalt900, Injected