db rating has been discussed before, check the custom exhaust thread in the NA section. (there are a few different points where they take a reading)
No, reread my above, I never said you cant buy them, I said they were discontinued. C-One don't have any in stock and no longer make them. hmm 65mm lets have a look at a real one, mines 66mm external diameter and 62mm internal....

did you not see the silencer???

Nengun, rhdjapan, fortyone auto. etc (online japanese part shops) lists parts, then you place an order, then they buy from the manufactures, then the shop sends it to you. Just because they have them listed on their website doesn't mean they have in stock or can order it in, since their websites aren't always up to date.
If I remember correctly you and I cant buy in a japanese yahoo auction unless you live in japan (I maybe be wrong). Then you will run into the problem of the muffler attachment C-One made to fit the exhaust for the BEAMS, since you'll need that aswell.
update:
some better detail shots of the exhaust (silencer out, then in)

This post has been edited by Rusty: Oct 2, 2010 - 1:42 AM