I mean, I've looked through everything; I can't find any earlier reference.

我尽力查阅所有相关文献,但我找不到更早的了

耶鲁公开课 - 金融市场课程节选

I just haven't been able to find a good program.

但我就是找不到好看的节目了。

Do you 实战 - SpeakingMax英语口语达人

but I can't find a good drama.

但我都找不到好看的电视剧了。

Do you 实战 - SpeakingMax英语口语达人