It's called the clutch slave cylinder. If you want one of the same quality (that lasted 20 years, lol), that would be an Aisin. They are $34 at autohausaz.com A decent cheaper alternative is the Beck/Arnley - $18 from rockauto.com
. Or you could get any old cylinder from a local parts store, but it won't be cheaper than the B/A and probably won't be as good. Another option, which I think would NOT be a good option, is a rebuild kit. That's only $10 from rockauto for the B/A kit (the best) but it won't do you any good if the cylinder is worn or corroded, and at 21 years, yours is probably both. So I wouldn't bother trying, and anyway, only 8 bucks cheaper than the complete cylinder.
Get a good DOT 4 brake fluid to completely flush the master & slave cyls. I like Valvoline SynPower which NAPA sells.
You may want to consider replacing the length of flexible rubber hydraulic line, since it's probably getting pretty tired, too.
And if you want to make a clean sweep, maybe the clutch master cyl also. Depends on how much preventative work you want to do, and how much $$ to spend. Check the stickied threads for hints on finding a factory service manual, which you absolutely should consult before doing the work.