Okay, here's Metrodorus, Fragment 5:
I just found this, and it also references Cicero so this may be a known fragment already.
(PS. I see it also references Epicurus Fragment 68 which has some similar wording. So, Metrodorus's contribution isn't earthshaking but does appear to be reinforcing.)
Nonetheless, there's our old friend κατάστημα right there (using the alternative c for sigma: κατάcτημα).
Using https://www.newadvent.org/fathers/02102.htm as a source for a translation of Metrodorus: "Metrodorus, in his book On the Source of Happiness in Ourselves being greater than that which arises from Objects, says: 'What else is the good of the soul but the sound state of the flesh, and the sure hope of its continuance?'"
The Greek for Metrodorus's quoted material is:
αγαθον, φησι ((he) says), ψυχης τι αλλο η το σαρκος ευσταθες καταστημα και το περι ταυτης πιστον ελπισμα.
Notes:
αγαθον ψυχης = "the good of the soul/psyche" Note also, is this "The Good" we've talked about elsewhere or just more like "for the benefit/good of the soul"?
το σαρκος ευσταθες καταστημα = "the sound state (katastema) of the flesh"
This is from