Go to this link:
https://kindle.amazon.com/your_reading
ALL your highlights and notes are listed there by book. So far as I know, there are NO limits to the amount stored there. You can then copy and paste from there to anywhere else.
Plus, you can read the highlights and notes of all other readers of that particular ebook if they have given permission to make their reading information public.
The only bug with that site is, if you remove one of your eBooks from it, you can never get it back there.