Onvia is supposed to be shipping mostly cbos right now, except out of one warehouse in CA, where almost all of the chips are reported to be the older stepping. I'm in Michigan, and I would have to be awfully unluckly to not get a shipment from EITHER PA or IL, as I am kind of in the middle of them, so I did not make a special shipping request. If you are in socal, I would definately make a special request.
If you must have a cbo (and we all must ), then my advice would be to either order there, or from another vendor that will specify cbo, OR, just go to a local computer show and read the numbers on the chips.
The link provided by the other poster will tell you the s-specs of all of the cbo and non-cbo PIIIs. With the exception of the chip that I just ordered from onvia, I always get them at computer shows. By physically reading the chips and looking for the right week and s-spec (gathered from information on intel's website and at
www.overclockers.com in the cpu database), I have managed to buy an unlocked PII 233 that did 300 at default voltage, a C300A that did 450+ at default voltage, and a whole tray of "good" retail bulk C366s (all but one did 550+ at between 1.8 and 2.1V).
Good luck,
Nack