If you are looking for the injectors go to ford. If you are just looking for the caps and o rings any auto parts store stocks them as a injector seal kit dont have a part # Keep that GN mostly stock and she will be worth some good money later.
There is a kit for 89 Sc's, you will have to open up the injector hole just a little with a drill bit. This will chamfer the hole more like the 94 style caps.
Niehoff or Borg Warner fuel injector seal kit:: 274081
about $2 each
I'd say most auto parts stores. I'd see who carries Niehoff. Like Kragen, Pepboys, Advanced Auto, Oreilly's, ... maybe Autozone. I'm not sure what's in your area, but you can order online from Kragen.com