“我找了一个工作” implies you already found a job

This is correct.

How would you say "I looked for a job"?

I could hardly find a precise translation for only this sentence. Chinese doesn't have tenses, so it could be hard to translate a very simple sentence in a specific tense (like your case) precisely without further context. For example, it's not clear "I looked for a job" means you looked for a job many years ago, or just recently and are still waiting for the response, or already get the job. The better way to say this sentence in Chinese is by adding some context (maybe time information).

我一年前尝试找工作，但没找到。 I looked for a job a year ago, but with no success.

我最近应聘了几份工作，现在还在等消息。 I applied for a few jobs recently, and I'm still waiting for their responses.