いい監督を探すのに3年費やしたが、見つからなかった。

、。

I spent three years searching for a good director, but I couldn't find one.

Literal

Good director [object-を] search [purpose-のに] 3 years spent [but-が], find-passive-not [past-だった].

~のに here is the purposive 'for the purpose of' (compare the clause-end 'although' のに). The の nominalizes 探す, and に marks it as the purpose. 費やす ('to spend, expend') is a formal verb for spending time, money, or effort. 見つかる ('to be found,' intransitive pair of 見つける) takes negative past here: 見つからなかった. Note が at the end of the first clause introduces soft contrast.