Pico 25 takes 25mm atties.
Fasttech claims to have them in stock in stainless/black, but I'm not sure how reliable fasttech is anymore, especially on this mod. It's a discontinued mod at this point.
Eleaf now has new Pico options that take over 22mm atties, the
Pico 2 &
Pico Plus
There's also the Pico 21700 and the Pico S (both take 18650 or 21700 batts) but they are a little bigger overall compared to the above. I believes these are also discontinued as well, though, so may be hard to find.