How can I get the latest version of safari for my windows 8.1 ?

Apple has not developed a Windows version of Safari for quite a few years. There is no version for Windows 8.1.

As Safari for Win was last updated in May 2012, it is full of security risks. Apple has taken it down from their website. Please do not be tempted to get it from some third-party download hosting site. In addition to Safari/Win no longer being secure, many download hosting sites will fix you up with malware/adware you rally don't want to have interfering with your computer's operation.