On Nar Shaddaa and Alderaan, you do the bonus series much later than the main quests there. Ergo, you've moved on to bigger and better medpacs. For some ungodly reason, bigger medpacs are not available, either by drop or purchase, in these bonus areas. Why??? It's not as if lower level characters could USE them if they ran over and got them in these bonus areas, they are level restricted. As it is, it reeks of an oversight/glitch, but the in-game help droid claims this is as it is intended to be. Why oh why oh why?