。
I'm looking for a present for mother.
Literal
Mother [for-に] present [obj-を] am-looking-for (polite).
Using に to mark the beneficiary of 探す is a slightly colloquial shortcut — more formally one might say 母へのプレゼント or 母にあげるプレゼント. The sentence works because the recipient-of-gift reading is strongly inferable from プレゼント, which is essentially always 'for someone.' Equivalent phrasings might also use の (母のプレゼント) when context disambiguates.