Respirocytes are a form of nanotechnology. Nanotechnology refers to the manipulation of substances on a nanometer scale, thus allowing design of machine at the molecular or even atomic level. Currently nanotechnology has only progressed to allow the assembly of relatively large, simple items. The earliest and most famous of these was IBM's arrangement of individual xenon atoms.
Within the next twenty years nanotechnology will advance greatly, and may be fully capable of producing tiny complex machines. The development of nanodevices that assemble other nanomachines will allow for massive cheap production. Thus respirocytes could be manufactured economically and abundantly.