I don't replace my tires when they wear as such, I move them somewhere else. So when the tires reach the wear indicators on my better bikes I shift them onto the rougher bikes, as they tend only to be used for local rides and therefore getting a puncture is less of a nuisance.
Some tires I remove and store when I obtain the bike or wheel they come on. For example, Stomil in Poland made bicycle tires until around 2005, so Stomil tires are getting rarer while the old bike scene is growing. My Stomils therefore await a better day. Saying that, if they are too rough then they get termed 'badgers' ('bald as a badger') and I have a pair of badly cracked 20" Stomil Antilopes on my gas bottle trailer and a pair of almost smooth 24" Stomil Zebras I sometimes use on my test wheels or as padding between my spare frames.
Tires, like coaster brake hubs, are a commodity.