Once again, **** you for being so funny.
You know, come to think of it, I'd probably say I don't like Petco much as a whole, just the Union Square location. Seems I like window-shop there every fortnight, and while most of the staff aren't exactly very knowledgeable, I've found Wayne to be quite helpful and friendly, even if he does look completely pissed-off all the time. The rest of the Petcos I've been to (Kips Bay and the two Brooklyn locations) are pretty awful.
And to answer your question (and to prove that I'm more helpful than a Petco employee.. if that means anything..), the only piece of CO2 equipment they carry is Jungle's CO2 bell system.