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...
:)
I've often thought the same, especially as the forces were gathered annually for the jamborees at the RAH. Ditto the ballet music which Watha used to conduct, I think. Oh well...