To download MSI-based installers for Adobe's free viewers/players, you must obtain a free license from Adobe.
See details here:
The Flash installer comes in two separate packages: one for Internet Explorer and one for Mozilla-based (Firefox, Seamonkey, etc.) browsers. Installation of the "plug-in" version (for Firefox) must take place after the installation of Firefox (duh).
Unattended install take the usual parameters:
msiexec /i <installer>.msi /qb
Applying patches is a bit more complicated, and getting the installer not to install shortcuts and other non-related junk over your system takes a bit more effort.