The standard "3" or "4" in the manuals could easily be made by you or a neighbor by welding a piece of 1-1/4 round to a flat bar with holes in it. I'd think that buying the IH Cub part, or buying a whole spring-trip standard, would be too expensive just for that piece. Though, agrisupply does sell these, http://www.agrisupply.com/Shank-For-Plo ... sid=&eid=/
I remember seeing on some supplier's website that they did sell half sweeps, but they just made them themselves by cutting of one wing of a full sweep.
It seems like the flexible c-shaped flat spring-steel things are often called shanks, and the solid ones standards (like spring-trip standards) but I don't think there's an official name really. For the business ends, it's my understanding that sweeps are the triangle-pointed ones (or whatever other shape) and shovels are the narrow pointed ones. Seems a bit backwards to me, but hey.