Alright, this got confusing quickly.
When Don said "chain store" he meant a store that sells chains (gold chain, silver chain, etc.), and he is saying if it specifically sells chains, the chances are slimmer that they'd carry the casing.
He was not referring to a "chain store" as a store with multiple franchises (McDonalds, Walmart, etc.)
Now there are some chain store chain stores, but that's a whole different story