GM developed magnetic dampers and are the ones licensing them to any other companies whose cars use them (like Ferrari and Ford). So it's highly unlikely we'll see any aftermarket companies sell them as an off the shelf unit anytime soon.
I did find this site that sells components:
LORD MR Products
and this one with less info
BWIGroup - Suspension - MAGNERIDE
Looks like you'd need pretty deep pockets and some custom fabrication work for these though.