Gti Cab - brake master cylinder reservoir

Hi all,

Desperately need a brake master cylinder reservoir. I can't get hold of a new one for at least a few weeks which is a big problem as it's meant to be in the Bodyshop tomorrow!! If any one can help or knows of a second hand one I'd be really grateful.

Thanks in advance 

Sorry, forgot to mention it's an 87 Gti Cab