If you can catch it oblique/early enough with a Block-1 upgrade ASTER-30 the SAMP-T or PAAMS would be more than adequate for midcourse intercept on the Iskander as my bet is that the missile is pretty much dumb on a GAINS strapdown.
Suck it up and do a UOR wet lease on some French kit.
Otherwise, you're left with ERINT on the MEADS PAC-3 system which may be a little lacking in terms of positive engagement overlaps before impact on that what, Mach 9? missile. I think that's what Spyder ended up being.
Of course, The Next Big Step is a Fluorine Laser ala MTHEL.
You're really just talking about an extraordinarily large CRAM mission here you know and the Nautilus was plucking 155mm Artillery shells out of midflight from 7km, even at at 2.25km/sec that's a 2 second engagement window, including through clouds. I seriously doubt if Iskander is going to be beating the tracking head on that.
Add to this, MTHEL was only 150KW. With SSLs you could slab up to 250KW in a hurry.
But be aware: If it will kill a seriously hypersonic missile in diver mode or a seriously supersonic contour follower, it will also put paid to subsonic airpower as well, unless the jets are operating at very great height as standoff (shoot the arrow, not the archer).
By the way, aren't there some key details between the SS-21/23 and the Iskander variant which prevent it from being nuclearized under INF? Or did they break the rules on that too?