Rav Dovid Feinstein shlit”a’s holding in the name of his father that it is mutar even when cy is readily available is not in the Igros either.
Right. I consider it on the level of being in the Igros. It is his own son.
And you keep asking for a source for the story, but what difference does it make? It’s not in the Igros.
Why would Rav Moshe tz”l recount the story in the Igros?
Also, where in Igros does it say that something which is not in the Igros is wrong?
There are teshuvas outside the Igros that can be different than in the Igros. The one’s in the Igros are usually the ones we follow.
And if you think that teshuvah is wrong, why did he write it?
It is not wrong. We just don’t know the circumstance he was writing in and everything.