Only one aftermarket supercharger kit was ever specifically designed and built for the MN12 4.6L engine and that was the Allen Supercharger kit. The Allen Supercharger company is no longer in business. You’re best bet to find one of these is to search on eBay, Craigslist or the classifieds of automotive forums.
As for the other supercharger companies, you’ll need to customize and modify their kits to fit your vehicle. As of today the FRPP SVO supercharger is a popular choice among MN12 enthusiasts with the SOHC 4.6L engine. The SVO is also no longer available for sale as a new unit but you can find them used. These superchargers are not inter-cooled and work best with a supplemental cooling mechanism such as water/methanol injection.
Lastly, note that most of these supercharger kits do not come to you as a complete kit for our cars and will require some fabrication to make them work. These kits are marketed toward the Mustang crowd. This thread was revised by TCCoA moderators and Admins, if we missed anything please send me a PM and I will correct any info.