If you need the flash player offline installer, you can download it from this official link:
http://get.adobe.com/flashplayer/otherversions/
you'd better download both the NPAPI and PPAPI if your environment has Firefox and Google Chrome deployed.
Then you got the offline installer! (Works on OSX 10.12.1. But if you are on OSX 10.11, you might still got the online installer, I tried on Safari, Firefox, Chrome, very odd!)
After the offline installer downloaded, open the dmg file, and show the contents of the install.app, you will find the pkg installer under /Contents/Resources/. Upload the pkg file to the Casper Admin and deploy it.
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As @Josh11.Smith said, we are not allow to distribute the flash player installer from the link above, this in NOT the Best Practice.