I just had quite a dismal thought. Harry is in disbelief the entire wizarding world is not pursuing the stone as priority one, which is a reasonable enough reaction.. Except.. How many wizards actually manage to die in their beds? Given the stated lifespan, and the cultural tendency to marry young, families ought to have a lot of generations alive at the same time.. but the older generations are thin on the ground. Harry was not raised by his grandparents! none of whom ought to have passed away from natural causes. Those elders we hear about are in the main fairly high up on the "competency/scary/power" scales. The logical implication being that wizards are not overly concerned about old age, because very few of them ever die from it. Something else - A dark lord, screwing up a spell, the magical wildlife, a succession dispute.. will get you first.. This logic could well deter a lot of people from attempting alchemy ; Succeeding in making a stone without being as good a survivor as Flamel carries a significant risk of dying now to violence instead of in 90 years to natural causes.

Of course, this also means that Flamel might not be very unique at all. If the stone is widely regarded as a nuisance magnet, successful crafters may be keeping a low profile.