Assuming they are the same as others used here (which I'm not sure of, but you seem sure they're quarter inch) - then you should be able to find a hydraulic specialist somewhere near you. There are a surprising number around, and they have large ranges of everything hydraulic.
They range from specialist 'Lockheed' agents, to the type of place which can supply service parts for anything from a JCB to a jumbo jet.
Here's one example:
http://www.powertrackbrakes.co.uk/index.html