for tips about playing and or adding multiphonics or dyads in your composition:
Multiphonics from the book The bass clarinet, a personal history (2012) by Harry Sparnaay
-> click HERE (sounding result = transposed, which means a none up)
Resources for composers by Heather Roche -> LINK
I like especially her list of dyads for clarinet (also notation = transposed) -> LINK