Where can I get more samples of dual passage ACT reading sections (and the new essay)? The official ACT folks have yet to release a book newer than their 2011 one. Princeton Review seems to only have one sample in their Cracking book (not even one in their practice tests in the back). Any advice?
For more ACT essay practice, I recommend reading my complete guide to ACT Writing prompts. In this article I not only list the two official ACT Writing prompts that have been released, but I also present four other prompts that I constructed, based on my dissection of the ACT Writing prompt.
Unfortunately, ACT, Inc. currently only has two publicly available examples of paired passage questions. As this article on answering paired passage questions mentions, the only places to find real ACT paired passage questions are on the ACT student site and in the Preparing for the ACT 2015-2016 guide. Fortunately, there are years of paired passages from the SAT that you can use to practice with to augment your studying - there's more information on just how to use SAT paired passages to prepare effectively for the ACT Reading in this article.
One other option for finding official(ish) ACT materials to practice with is discussed in this article. There are several official old ACT tests available for free online that have not actually been released by the ACT. Mostly they're the result of students getting their ACT tests back through Test Information Release and then deciding to upload them online for others to use. The sites these tests are on are technically breaking some intellectual property and copyright rules; as Anna says in the article, as long as you refrain from loudly proclaiming what you've done, you'll probably be fine, but beware of this.
That said, here would be the ACT tests to look for, if you want more actual ACTs to practice from:
For the essay: December 2015, April 2016, June 2016, December 2016, etc (only the first one is probably available right now, but you get the picture).
For paired passages: June 2014, December 2014, April 2015, June 2015, December 2015, and so on.
For all of these tests, you can check the form number (e.g. 72E) to make sure the tests aren't a duplicate of one you've used to practice with already.