[quote author=wikipedia]
The 200 mm f/1.8 USM lens, introduced in November 1988, is the fastest 200mm ever produced.[1] It is a large off-white lens with rear drop-in filter tray. Production was discontinued in 2004. Its total production run was 8,000 with serial numbers from 11,000 to 17,999 inclusive[/quote]
There were plenty made, so there should be some coming up for sale from time to time. But if you do buy one, make sure the date code shows its one of the later ones to come off the production line - the electronics in the earlier samples will be very likely to fail soon, with a very expensive repair bill to match.
I know these two lenses are tested on different bodies, but its quite clear that the 200/1.8 stopped down to f2.0 doesn't offer anywhere near the same level of per-pixel detail as the IS equipped 200/2 does wide open:
Canon stopped servicing them some years ago, and now various parts are unavailable, the main reason I sold mine a few years back.
Awesome lens, though. Hugely front-heavy.