Hey, that sounds familiar... My car had sat for a long time, and I was able to just rebuild the clutch master cylinder. The clutch master is NLA, but it can be easily and cheaply rebuilt w/a kit. Of course (and on the downside), you'll have to first remove it and make sure that the bore is not terribly scarred up/rusted, but once it's out, it's easy to do. It comes out easily, but is a bit of a PITA to get it back in yourself.
If this isn't for you, there are suppliers in the "Links" area that can also help you with either a good used, or maybe a rebuilt one.
Lastly, there was a Q&A sent in to the Roundel some issues back regarding cross-referencing part numbers for NLA parts that could possibly be substituted; the clutch master and slave for E3/E9 was the topic of the cross-reference question. Maybe someone knows if an E12/E24 master may work...
Either way you go, good luck.
Regarding the slave cylinder, it can be purchased new.