I'm not going to exactly answer your question on where you can get them, but instead I hope to persuade you not to get them.
The SAT (as well as the ACT) is just a measurement of your strengths and weaknesses in subjects and you shouldn't cheat on it or else it'll inaccurately project how well you did. We all want to get high scores, I truly get that. I mean, I just finished taking all those tests less than half a year ago, so I know what you're going through! But if you submit something that is false, it will hurt you in the long run. Yeah you might get accepted to that Ivy League you've always dreamed of going to, but if you actually aren't ready for that, then you will suffer the consequences. The college doesn't have to know that you cheated, but deep down you will struggle to keep up or you'll have a hard time understanding your classes. All that stress will build up and you will eventually break down. That's why it is important to do YOUR best instead of trying to fake it through by cheating.
Second of all, high school, the CollegeBoard (those who make SAT and AP tests), and the ACT people makes it sound like the SAT and ACT are a HUGE DEAL. They can be, but mostly they are just a guide for college admissions people to quickly glance at your profile and put you either in the "in consideration" pile or not. Admissions for colleges go through HUNDREDS OF THOUSANDS of applications. They can't read all of your essays so they rely on your scores to decide whether you are worth looking over or not. After you get into the "in consideration" pile, admissions don't care about your scores anymore. They look at your essays, your grades, your resume, and all that jazz. So in the end, your scores aren't as important as you think they are. That doesn't mean you should slack off; it just means that you shouldn't stress yourself out to the point where you consider cheating as your only option.