The Copperhead must have been discontinued as Razer no longer lists it as one of their products on their website. It still shows up in some stores (including their own) but my guess is they're just selling out the last of the inventory and not producing any more new ones. I have also noticed that the Diamondback 3G is becoming ever harder to find, which wouldn't surprise me if Razer is going to discontinue or at least update this brand name, they've done it before with the Diamondback and have most recently done it to the DeathAdder (and Salmosa as well, but with a name change to the Abyssus, as the Abyssus is essentially the same shape/size with the same general feature set, the pirmary difference is the sensor)
Now, seeing as how the Diamondback is more of a finger tip mouse, if you're really attached to the form and the features your best bet really would be to stick with a Diamondback 3G or a Copperhead as both share a very similar size and form factor, granted both have actually fallen pretty far behind the curve in terms of gaming grade mousing features.
Of course this all really does depend on how exactly you grip the mouse when playing:
Palm - the entirety (or most of it) of your hand lays in direct contact with the mouse when gripping it
Claw - fingers are arched with the lower portion of your palm making contact with the mouse so that only the tips of your fingers and part of your palm are making direct contact with the mouse while gripping
Finger - grip is pretty much strictly with finger tips only