。
I can't find what I'm looking for.
Literal
Want [attributive-の] things [subject-が] find-cannot-[explanatory-んだ].
Passive-like potential: 見つかる ('to be found / to turn up') is actually the intransitive of 見つける ('to find [actively]'). 見つからない = 'won't turn up / can't be found.' Japanese often prefers this intransitive framing over the explicit potential of the transitive. んだ frames it as a shared explanation.