I'd consider the sagas, which would be good at flash speed because you can generally surprise the table and trigger the second chapter.
For your deck specifically, I'd consider:
- Fall of the Thran: meta dependent, of course, but you can make it so that you destroy all lands at instant speed, and you rebuild much faster.
- The Antiquities War: your artifact count is 18, but you also have 10 artifact creatures. I think a count of 28 artifacts is enough to justify running this one.
Have you considered them? I have tried them, but I like Phyrexian Scriptures best, and obviously you can't use it.