The Mazda hardtop fitting kit can be purchased from mx5parts but costs about £350. It includes the Frankenstein bolts for the rear deck, new interior side panels, side brackets and wiring harness for the heated rear window.
A cheaper alternative especially for winter use were you wont want to keep removing the top every weekend is to use the jazz brackets which cost about £100 for both front and side brackets, you would still require the Frankenstein bolts and the wiring harness both of which can be purchased seperately. The jazz kit requires removal of the hardtop front fittings. Alternatively you can just use the jazz side brackets and retain the orginal hardtop front brackets to save even more cost.