A wired idea: Are there any Chinese idioms dictionary which is specific to translate a English word?
You can search the app store, like google play. There are loads of idiom dictionaries you can try.

And like other people commented I don't think your translation of '如獲至寶' is proper. Serendipity is valuable discoveries are made by accident or luck. But '如獲至寶' is finding something which is very valuable, it can be found this thing by accident, but this idiom's main idea is emphasis find something very important. Maybe 机缘巧合 is better.