Is it possible to disable Ctrl + F of find in page?

I would presume that using keydown would enable this, however as a matter of principle, changing the way that a browser behaves is a bad idea. Although it is more of a pain for you to do, there are font replacement techniques that should make it easier.

If you do find a means of doing this, there is always a danger that someone will get around it. It is far better to write the page to work whatever than hack the browser.