Note that I have also answered this question here: How do I get NSTextFinder to show up
The problem is that findBarVisible only sets the visibility of the bar through it's container, it does not actually tell the NSTextFinder itself that it needs to show up (at least, that is my understanding of it).
Assuming that you have your textFinder client set up properly, and your scrollview category set up properly, you still need to implement an action to make it appear. Then you should be able to make it appear and disappear at will.
Replace [self.webView scrollView].findBarVisible = YES;
with
[self.textFinder performAction:NSTextFinderActionShowFindInterface];
Also, note that I have the NSTextFinder as an IBAction created in the XIB file. I'm not sure if that prevents it from appearing or not.