It's not stock music. It was composed by Fred Steiner as a replacement for Comstock's theme when the show moved to NBC in 1961, and the 1997 prints used it to avoid paying royalties to Comstock's estate. More details here: reddit.com/r/FrostbiteFalls/comments/1flr8ue/frank_comstock_and_the_bullwinkle_music_that_got/