There are a ridiculously large number of text editors and note apps in the App Store, so there's bound to be a few.
Here's my list, with the ones that have a Find & Replace option.
- Pages: Actually this is Apple's (nearly) full featured word processor. Saves in it's own native format, but can import/export .doc.
- Storyist: Optimized for writing scripts and/or novels. Very nice if you need the kind of cross indexing, notes, and standard formatting common in those types of writing.
- Textilus: Full featured text editor with support for rtf, markdown, plain text, HTML, and more.
They all work slightly differently, but in every case you have to tap through the results and confirm/replace them. It's the safest method, but could get old if you are replacing all semicolons with colons.
I also have Daedalus, but I can't find a Find feature in it. Ironically this is the one I use the most when Notes, Evernote, or Pages does not fill the need. It has a kind of free flowing page stack style that makes it easy to fiddle with writing ideas.
I'm sure there are many others, and I hope you you get some more suggestions.
Goog luck.