I have MP3s of both "Hiawatha's Wedding Feast" and "The Death of Minnehaha" conducted by Sargent in good recordings. Let me know if you need them. In the meantime, the Argo (Kenneth Alwyn) set is the one to go for, although there's also an excellent performance of the whole shebang from a Three Choirs Festival performance in the archive (PM me). It's odd that Sargent didn't record "Hiawatha's Departure" to complete the trilogy...
:)
BTW, I have the Three Choirs recording from the archive you mention and agree that it's very good.