These came with a damper/spring kit sold by Bilstein, but I had to use a different spec spring for my class. Includes 2 fronts, 2 rears, 2 helper springs & the aluminum sliding abutments between the helpers & front strings.
Front Main Spring: E4-FD1-Y412A00 (340lbs/in)
Rear Main Spring: E4-FD1-Y805A00 (240lbs/in)
Front Tender Spring: E4-FD1-Y504A01 (80lbs/in)
These appear to be twice as stiff than the progress springs, if that is what you are looking for.
$150 plus shipping.
mx5 (at) leisurehound (dot) com