I've found that one support spring can last through two, maybe three, hoses. If I replace a lower hose and the new one has the coil in it, I'll remove the old one, clean most of the crud off of it, and hang it on a hook out in the garage for "just in case."
Typically, the lower hose will collapse with age - the rubber softens from exposure to heat and oil, and will give out under suction from the water pump. Having the support coil in the hose is cheap insurance, and can make the difference between driving home and walking home at times.
If you just can't find a new spring when you need one, check at hydraulic shops. Suction lines for "primary power pumps" are often lined with support coils, which are available separately. The ones used for fluid power are typically CRES (vice chrome- or zinc-plated carbon steel,) and are usually wound from a thin, flat bar instead of simple wire. Get one of these, cut it to length, and you could use it for probably the rest of the life of the vehicle - I just haven't tried yet.