I think most people find them from sites like https://www.cursors-4u.com/
If you find one you like from that page, copy the code from Option #2 (CSS Style Sheet Only)
and make sure you paste it between two <style> </style> indicators. It should look something like this:
<style>
* {
cursor: url(https://ani.cursors-4u.net/cursors/cur-13/cur1149.ani), url(https://ani.cursors-4u.net/cursors/cur-13/cur1149.png), auto !important;
}
</style>