Also using Tom Lee's search phrases, try the Apple Support website and click the "Include archive" option after you perform the search. You have to keep doing it for every new search.

Also Search for "hd-20SC" and "HD SC".

Apple did not make the drive mechanism, but they did manufacture the assembled unit. The internal drives in the SC series were supplied by a variety of drive manufacturers. Introduced in September 1986 along with the Apple IIGS.

Apple only built one hard drive, the Widget used only in the Lisa 2/Mac XL. AFAIK the only other drive Apple built was the Twiggy used only in the Lisa 1.