They aren't that hard to find but almost always bring a premium price. They aren't particularly rare (16's) but there seems to be a constant demand for them which is what pushes the price up. 14" floors are tougher to find and go for even more...and Jazz Festivals...well good luck should you ever decide to hunt for one of those at a "reasonable" price.
The ones that constantly sit on ebay are priced too high (the sellers apparently hope somebody might pay that if they get desperate enough or don't care about money). Most sellers aren't totally oblivious to the "Ringo factor" though so unless you get lucky you should figure you're going to have to spend more $ for a Oyster Black 16 than a blue sparkle one.