Well, You have just got started.
1- front struts/ball joints
2- tire balance/ tires, even tire pressures
3- alignment( critical)
4- steering sector/adjustment
5- double jointed shaft from steering shaft to sector(2 u-joints)
6- all tie rods ends , drag link
I don't know what you have checked already, but any one of these items can cause big time shimmy. Supers have a nasty habit of spreading the pain around. You can have one item wear out and if you don't correct it , the shimmy will shake everything else to death over a period of time then you just about have to replace everything that moves up front. Its hard to just replace one thing at a time. When you get around to fixing the other stuff, the first thing you replaced 6 months ago has already destroyed itselve again from the shaking.
Soooooooooo ?