For the most part, yes, they mean the same things.
However, "I find" is more of a feeling that you have and is often used in general situations. It's kind of like saying "Looking at my past experiences, it would be hard for me to believe..."
On the other hand, "I think" is more of an opinion. It would be saying something like "I think, and for that matter others might think as well, that it is hard to believe..."