Mate uses themes and mouse pointers of gnome2 (gtk2 actualyactually), so a good place to start looking is gnome-look.org , here you can find many themes for the mouse pointer to install, and it works, I use mate myselvemyself.
After downloading the theme file (do not extract it!) go to the appearance screen of gnome/mate or mate, there you have a install button, use it to install the downloaded theme. afterwardsafterward you can go to customize to change it.