The Spanish hallar (“to find”) comes from the Latin afflare (“to blow.”) From that same Latin root we get various f‑l words involving blowing, including:

All of these share the f‑l root. But how did this turn into the Spanish hallar? Well, first remember that the initial F- sound tended to disappear when Latin turned into Spanish; see, fig and higo or fable and hablar. Secondly, note that finding something is just blowing on it, uncovering what was below the dust you blew away!