It’s a little hard to find copies of prep guides for each year since it’s so niche. I had copies over a decade ago but those are probably useless now. In general its really hard to get pirated technical books, I’ve had some luck with Library Genesis, Z Library, Liber3, or project Gutenburg.
An alternative to look at might be doing all of the AP High School and College subjects on KhanAcademy. And practice handwritten essays if you intend to take the optionals.
TBH scoring a 30 or higher on the ACT is a lot easier than scoring high on the SATs. None of the subjects will ask you to solve multivariate differential equations or anything high level like that.