There're very few websites that offer SAT Subject Test sample papers for free. It's super hard to find the sample papers of SAT Subject Tests online as College Board doesn't release the SAT Subject Test sample papers officially.
But CB released the Subject Test sample papers in the book format. So it's not accessible to the students mostly.
You have to buy the books individually to access all the Subject Test sample papers.
It has been circulating that Subject Test practice papers answer explanations are unsatisfactory. I am not sure about it.
If that's the case, i have known a prep company called TestprepKart. They made the video solutions of all those 8 Subject Tests sample papers. You can [url=https://www.testprepkart.com/campaign/sat-test-series-&-solutions.php]buy online SAT Subject Test series[/url] here.