If you need the flash player offline installer, you can download it from this official link:
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.
As @Josh.Smith said, we are not allow to distribute the flash player installer from the link above, this in NOT the Best Practice.
@Steven.Xu That is a nice link, thanks for sharing. I'd like to disagree that this would be "Best Practice" though, for two reasons:
3.3 Distribution. This license does not grant you the right to sublicense or distribute the Software. For information about obtaining the right to distribute the Software on tangible media or through an internal network or with your product or service. please refer to http://www.adobe.com/go/acrobat_distribute for information about Reader, or http://www.adobe.com/go/licensing for information about the Adobe Runtimes.
Sign up for a free license to distribute Flash (https://www.adobe.com/products/flashplayer/distribution.html) and then either download from the distribution site or use AutoPkg(r)!
If you sign up your organization at the distribution link that @Josh.Smith mentioned, you're given a "distribution4" URL that is specific for your organization, and that gets you access to the pkg installers.
Barring that, there is an AutoPkg recipe for the regular NPAPI Flash Player, but none for the PPAPI one as far as I'm aware...