You couldn't buy just the kit, it was a dealer option in Germany and via Silver knight in the UK when you wanted to buy a new Mk1, Toyota commissioned Haslbeck to make the kit and was offered in the dealership as a Haslbeck special edition or "Mr2 High Tech" as it was known in Germany at the time. My best guess is Toyota would deliver a brand new Mk1 to Haslbeck for the kit fitting.

That is what makes this kit so special compared to aftermarket stuff, it's the MK1 version of a Mk2 TRD kit I suppose.